Protocol for the Examination of Specimens From Patients With Primary Carcinomas of the Colon and Rectum

Abstract

The College of American Pathologists offers these protocols to assist pathologists in providing clinically useful and relevant information when reporting results of surgical specimen examinations. The College regards the reporting elements in the “Surgical Pathology Cancer Case Summary (Checklist)” portion of the protocols as essential elements of the pathology report. However, the manner in which these elements are reported is at the discretion of each specific pathologist, taking into account clinician preferences, institutional policies, and individual practice.The College developed these protocols as an educational tool to assist pathologists in the useful reporting of relevant information. It did not issue the protocols for use in litigation, reimbursement, or other contexts. Nevertheless, the College recognizes that the protocols might be used by hospitals, attorneys, payers, and others. Indeed, effective January 1, 2004, the Commission on Cancer of the American College of Surgeons mandated the use of the checklist elements of the protocols as part of its Cancer Program Standards for Approved Cancer Programs. Therefore, it becomes even more important for pathologists to familiarize themselves with the document. At the same time, the College cautions that use of the protocols other than for their intended educational purpose may involve additional considerations that are beyond the scope of this document.This protocol applies to all primary carcinomas of the colon and rectum. Well-differentiated neuroendocrine neoplasms (carcinoid tumors) are not included. The American Joint Committee on Cancer (AJCC)/International Union Against Cancer TNM classification system is recommended.Check 1 Response Unless Otherwise IndicatedTumor Site (note A)__ Cecum__ Right (ascending) colon__ Hepatic flexure__ Transverse colon__ Splenic flexure__ Left (descending) colon__ Sigmoid colon__ Rectum__ Not specified*Specimen Integrity*__ Intact*__ Fragmented*Polyp Size*Greatest dimension: __ cm*Additional dimensions: __ × __ cm*__ Cannot be determined (see Comment)*Polyp Configuration*__ Pedunculated with stalk *Stalk length: __ cm*__ SessileSize of Invasive CarcinomaGreatest dimension: __ cm*Additional dimensions: __× __ cm__ Cannot be determined (see Comment)Histologic Type (note B)__ Adenocarcinoma__ Mucinous adenocarcinoma__ Signet-ring cell carcinoma__ Small cell carcinoma__ Squamous cell carcinoma__ Adenosquamous carcinoma__ Medullary carcinoma__ Undifferentiated carcinoma__ Other (specify): __________________ Carcinoma, type cannot be determinedHistologic Grade (note C)__ Not applicable__ Cannot be determined__ Low-grade (well differentiated to moderately differentiated)__ High-grade (poorly differentiated to undifferentiated)Tumor Extension (note D)__ Cannot be determinedInvasion (Deepest)__ Lamina propria__ Muscularis mucosae__ Submucosa__ Muscularis propriaMargins (check all that apply)Deep Margin (Stalk Margin)__ Cannot be assessed__ Uninvolved by invasive carcinoma Distance of invasive carcinoma from margin: __ mm__ Involved by invasive carcinomaMucosal/Lateral Margin__ Not applicable__ Cannot be assessed__ Uninvolved by invasive carcinoma__ Involved by invasive carcinoma__ Involved by adenomaVenous (Large Vessel) Invasion (V) (note E)__ Not identified__ Present__ IndeterminateLymphatic (Small Vessel) Invasion (L) (note F)__ Not identified__ Present__ Indeterminate*Type of Polyp in Which Invasive Carcinoma Arose (note G)*__ Tubular adenoma*__ Villous adenoma*__ Tubulovillous adenoma*__ Traditional serrated adenoma*__ Sessile serrated adenoma*__ Hamartomatous polyp*__ Indeterminate*Additional Pathologic Findings (check all that apply)*__ None identified*__ Inflammatory bowel disease *__ Active *__ Quiescent*__ Other (specify): ________________*Ancillary Studies*Specify: ________________*__ Not performed*Comment(s): ________________Check 1 Response Unless Otherwise IndicatedSpecimen (check all that apply) (note A)__ Terminal ileum__ Cecum__ Appendix__ Ascending colon__ Transverse colon__ Descending colon__ Sigmoid colon__ Rectum__ Anus__ Other (specify): __________________ Not specifiedProcedure__ Right hemicolectomy__ Transverse colectomy__ Left hemicolectomy__ Sigmoidectomy__ Rectal/rectosigmoid colon (low anterior resection)__ Total abdominal colectomy__ Abdominoperineal resection__ Transanal disk excision (local excision)__ Other (specify): __________________ Not specified*Specimen Length (if applicable)*Specify: __ cmTumor Site (check all that apply) (note A)__ Cecum__ Right (ascending) colon__ Hepatic flexure__ Transverse colon__ Splenic flexure__ Left (descending) colon__ Sigmoid colon__ Rectosigmoid__ Rectum__ Colon, not otherwise specified__ Cannot be determined (see Comment)Tumor SizeGreatest dimension: __ cm*Additional dimensions: __ × __ cm__ Cannot be determined (see Comment)Macroscopic Tumor Perforation (note H)__ Present__ Absent__ Cannot be determined*Macroscopic Intactness of Mesorectum (note I)*__ Not applicable*__ Complete*__ Near complete*__ Incomplete*__ Cannot be determinedHistologic Type (note B)__ Adenocarcinoma__ Mucinous adenocarcinoma__ Signet-ring cell carcinoma__ Small cell carcinoma__ Squamous cell carcinoma__ Adenosquamous carcinoma__ Medullary carcinoma__ Undifferentiated carcinoma__ Other (specify): __________________ Carcinoma, type cannot be determinedHistologic Grade (note C)__ Not applicable__ Cannot be assessed__ Low-grade (well differentiated to moderately differentiated)__ High-grade (poorly differentiated to undifferentiated)__ Other (specify): ________________*Histologic Features Suggestive of Microsatellite Instability (note J)*Intratumoral Lymphocytic Response (Tumor-Infiltrating Lymphocytes)*__ None*__ Mild to moderate (0–2 per high-power [×400] field)*__ Marked (3 or more per high-power field)*Peritumor Lymphocytic Response (Crohn-like Response)*__ None*__ Mild to moderate*__ Marked*Tumor Subtype and Differentiation (check all that apply)*__ Mucinous tumor component (specify percentage: __%)*__ Medullary tumor component*__ High histologic grade (poorly differentiated)Microscopic Tumor Extension__ Cannot be assessed__ No evidence of primary tumor__ Intramucosal carcinoma, invasion of lamina propria__ Tumor invades submucosa__ Tumor invades muscularis propria__ Tumor invades through the muscularis propria into the subserosal adipose tissue or the nonperitonealized pericolic or perirectal soft tissues but does not extend to the serosal surfaceMaximal Extension (check all that apply)__ Tumor directly invades adjacent structures (specify): __________________ Tumor microscopically involves the serosal surface (visceral peritoneum)Margins (check all that apply) (note K)Proximal Margin__ Cannot be assessed__ Uninvolved by invasive carcinoma__ Involved by invasive carcinoma__ Intramucosal carcinoma/adenoma absent at proximal margin__ Intramucosal carcinoma/adenoma present at proximal marginDistal Margin__ Cannot be assessed__ Uninvolved by invasive carcinoma__ Involved by invasive carcinoma__ Intramucosal carcinoma/adenoma absent at distal margin__ Intramucosal carcinoma/adenoma present at distal marginCircumferential (Radial) or Mesenteric Margin__ Not applicable__ Cannot be assessed__ Uninvolved by invasive carcinoma__ Involved by invasive carcinoma (tumor present 0– 1 mm from margin)If all margins uninvolved by invasive carcinoma:Distance of invasive carcinoma from closest margin: __ mm OR __ cmSpecify margin: ________________Lateral Margin (for Noncircumferential Transanal Disk Excision)__ Cannot be assessed__ Uninvolved by invasive carcinoma Distance of invasive carcinoma from closest lateral margin: __ mm *Specify location (eg, o'clock position), if possible: __________________ Involved by invasive carcinoma *Specify location (eg, o'clock position), if possible: __________________ Uninvolved by adenoma__ Involved by adenomaTreatment Effect (applicable to carcinomas treated with neoadjuvant therapy) (note L)__ No prior treatment__ Present *__ No residual tumor (complete response, grade 0) *__ Marked response (grade 1, minimal residualcancer) *__ Moderate response (grade 2)__ No definite response identified (grade 3, poor or no response)__ Not knownVascular (Large Vessel) Invasion (V) (check all that apply) (note E)__ Not identified__ Present__ IndeterminateLymphatic (Small Vessel) Invasion (L) (check all that apply) (note F)__ Not identified__ Present__ Indeterminate*Discontinuous Extramural Extension (irregular tumor nodules in pericolorectal adipose tissue without histologic evidence of residual lymph node) (note M)*__ Not identified*__ Present*__ Cannot be determined*Perineural Invasion (note F)*__ Not identified*__ Present*Type of Preexisting Polyp in Which Invasive Carcinoma Arose (note G)*__ None identified*__ Tubular adenoma*__ Villous adenoma*__ Tubulovillous adenoma*__ Traditional serrated adenoma*__ Sessile serrated adenoma*__ Hamartomatous polyp*__ IndeterminatePathologic Staging (pTNM) (note N)TNM Descriptors__ None__ m (multiple primary tumors)__ r (recurrent)__ y (posttreatment)Primary Tumor (pT)__ pTX: Cannot be assessed__ pT0: No evidence of primary tumor__ pTis: Carcinoma in situ, intraepithelial (no invasion)__ pTis: Carcinoma in situ, invasion of lamina propria__ pT1: Tumor invades submucosa__ pT2: Tumor invades muscularis propria__ pT3: Tumor invades through the muscularis propria into the subserosa or the nonperitonealized pericolic or perirectal soft tissues__ pT4a: Tumor penetrates the visceral peritoneum__ pT4b: Tumor directly invades other organs or structuresRegional Lymph Nodes (pN)__ pNX: Cannot be assessed__ pN0: No regional lymph node metastasis__ pN1: Metastasis in 1 to 3 regional lymph nodes__ pN2: Metastasis in 4 or more regional lymph nodesSpecify: Number examined: __ Number involved: __Distant Metastasis (pM)__ Cannot be assessed__ pM1: Distant metastasis *Specify site(s):________________*Additional Pathologic Findings (check all that apply)*__ None identified*__ Adenoma(s)*__ Chronic ulcerative proctocolitis*__ Crohn disease*__ Dysplasia arising in inflammatory bowel disease*__ Other polyps (type[s]): ________________*__ Other (specify): ________________________________*Ancillary Studies (note O)*Specify: ________________*__ Not performedComment(s): ________________* Data elements with asterisks are not required for accreditation purposes for the Commission on Cancer. These elements may be clinically important, but are not yet validated or regularly used in patient management. Alternatively, the necessary data may not be available to the pathologist at the time of pathologic assessment of this specimen.The protocol applies to all carcinomas arising in the colon and rectum.1 It excludes carcinomas of the vermiform appendix.The colon is divided as shown in Figure 1. The right colon is subdivided into the cecum and the ascending colon.2 The left colon is subdivided into the descending colon and sigmoid colon (Table).1The transition from sigmoid to rectum is marked by the fusion of the tenia coli of the sigmoid to form the circumferential longitudinal muscle of the rectal wall approximately 12 to 15 cm from the dentate line.1 The rectum is defined clinically as the distal large intestine commencing opposite the sacral promontory and ending at the upper border of the anal canal (Figure 2). When measuring below with a rigid sigmoidoscope, it extends 16 cm from the anal verge.Tumors located at the border between 2 subsites of the colon (eg, cecum and ascending colon) are registered as tumors of the subsite that is more involved. If 2 subsites are involved to the same extent, the tumor is classified as an “overlapping” lesion.A tumor is classified as rectal if its inferior margin lies less than 16 cm from the anal verge or if any part of the tumor is located at least partly within the supply of the superior rectal artery.3 A tumor is classified as rectosigmoid when differentiation between rectum and sigmoid according to the previous guidelines is not possible.4For consistency in reporting, the histologic classification proposed by the World Health Organization is recommended and is shown in the following.5AdenocarcinomaMucinous (colloid) adenocarcinoma (greater than 50% mucinous)Signet-ring cell carcinoma (greater than 50% signet-ring cells)*Squamous cell carcinomaAdenosquamous carcinomaMedullary carcinoma†Small cell carcinoma* (high-grade neuroendocrine carcinoma)Undifferentiated carcinoma*Other (specify)‡* By convention, signet-ring cell carcinomas, small cell carcinomas, and undifferentiated carcinomas are high grade (see note C). The only histologic types of colorectal carcinoma that have been shown to have adverse prognostic significance independent of stage are signet-ring cell carcinoma67 and small cell carcinoma (high-grade neuroendocrine carcinoma).8† Medullary carcinoma is a distinctive histologic type strongly associated with high levels of microsatellite instability (MSI-H), indicative of defects in normal DNA repair gene function.910 Medullary carcinoma may occur either sporadically11 or in association with hereditary nonpolyposis colon cancer (HNPCC).10 This tumor type is characterized by solid growth in nested, organoid, or trabecular patterns, with no immunohistochemical evidence of neuroendocrine differentiation.11 Medullary carcinomas are also characterized by numerous tumor infiltrating lymphocytes (see note J).‡ The term “carcinoma, NOS” (not otherwise specified) is not part of the World Health Organization classification.A number of grading systems for colorectal cancer have been suggested, but a single widely accepted and uniformly used standard for grading is lacking. Most systems stratify tumors into 3 or 4 grades as follows.Grade 1 Well differentiatedGrade 2 Moderately differentiatedGrade 3 Poorly differentiatedGrade 4 UndifferentiatedDespite a significant degree of interobserver variability,12 histologic grade has repeatedly been shown by multivariate analysis to be a stage-independent prognostic factor.13 Specifically, it has been demonstrated that high tumor grade is an adverse prognostic factor. It is noteworthy that in the majority of studies documenting the prognostic power of tumor grade, the number of grades has been collapsed to produce a 2-tiered stratification for data analysis as follows.Low grade—Well differentiated and moderately differentiatedHigh grade—Poorly differentiated and undifferentiatedThe widest variations in grading concern the stratification of low-grade tumors into well- or moderately differentiated categories, whereas interobserver variability in diagnosing high-grade carcinoma is relatively small. Therefore, in light of its proven prognostic value, relative simplicity, and reproducibility, a 2-tiered grading system for colorectal carcinoma (ie, low grade and high grade) is recommended. The following criteria for grading based on gland formation alone are suggested.14Low grade—Greater than or equal to 50% gland formationHigh grade—Less than 50% gland formationColorectal adenomas containing invasive adenocarcinoma that extends through the muscularis mucosae into the submucosa have been defined as “malignant polyps.” This term encompasses cases in which the entire polyp head is replaced by carcinoma and adenomas with focal malignancy, but the definition excludes adenomas with high-grade dysplasia (intraepithelial carcinoma) or intramucosal carcinoma (invasive carcinoma limited to the lamina propria or invading no deeper than the muscularis mucosae), because these polyps possess negligible biologic potential for metastasis (see Tis in note N).Malignant polyps removed by endoscopic polypectomy require evaluation of histologic factors related to the risk of adverse outcome (ie, lymph node metastasis or local recurrence from residual malignancy) following polypectomy.15–18 Factors shown to have independent prognostic significance and that are important in determining the need for further surgical treatment include the following.An increased risk of adverse outcome has been shown to be associated with the following.Venous invasion has been demonstrated by multivariate analysis to be an independent adverse prognostic factor.13 Invasion of extramural veins, in particular, has been shown to be an independent indicator of unfavorable outcome and increased risk of occurrence of hepatic metastasis.19The significance of intramural venous invasion is less clear, because data specific to this issue are lacking. Nevertheless, it is recommended that the presence or absence of venous invasion and its anatomic location should be reported in all cases.14Venous invasion is coded as follows in the AJCC staging system.Venous Invasion (V)VX Venous invasion cannot be assessedV0 No venous invasionV1 Microscopic venous invasionV2 Macroscopic venous invasionIn several studies, both lymphatic invasion20 and perineural invasion21 have been shown by multivariate analysis to be independent indicators of poor prognosis. The prognostic significance, if any, of the anatomic location of these structures is not defined. Furthermore, it is not always possible to distinguish lymphatic vessels from postcapillary venules, because both are small, thin-walled structures. Thus, the presence or absence of tumor invasion of small, thin-walled vessels should be reported in all cases, and its anatomic location within the colonic wall noted.14Lymphatic invasion is coded as follows in the AJCC staging system.Lymphatic Vessel Invasion (L)LX Lymphatic vessel invasion cannot be assessedL0 No lymphatic vessel invasionL1 Lymphatic vessel invasionDistinction should be made between traditional serrated adenomas, which exhibit cytologic features of adenomas, and the newly described sessile serrated adenomas.22 The sessile serrated adenoma may be the precursor lesion for colorectal carcinomas with high levels of microsatellite instability; they are more commonly found in the right colon and are characterized by serrated architecture with bulbous dilatation of deep crypts and lack of overt nuclear atypia, in most cases.Tumor perforation is an uncommon complication of colorectal cancer, but one that is associated with a poor outcome, including high in-hospital mortality and morbidity.23 Perforation of the uninvolved colon proximal to an obstructing tumor is also associated with high mortality because of generalized peritonitis and sepsis. Reported perforation rates range from 2.6% to 9%. Perforation is more likely to occur in older patients.The quality of the surgical technique is a key factor in the success of surgical treatment for rectal cancer, both in the prevention of local recurrence and in long-term survival. Numerous studies have demonstrated that total mesorectal excision improves local recurrence rates and the corresponding survival by as much as 20%. This surgical technique entails precise sharp dissection within the areolar plane outside (lateral to) the visceral mesorectal fascia to remove the rectum. This plane encases the rectum, its mesentery, and all regional nodes and constitutes Waldeyer fascia. High-quality total mesorectal excision surgery reduces local recurrence from 20% to 30% to 8% to 10% or less and increases 5-year survival from 48% to 68%.2425 Adjuvant therapy in the presence of a high-quality total mesorectal excision may further reduce local recurrence (from 8% to 2.6%).25Pathologic evaluation of the resection specimen has been shown to be a sensitive means of assessing the quality of rectal surgery. It is superior to indirect measures of surgical quality assessment, such as perioperative mortality, rates of complication, number of local recurrences, and 5-year survival. It has been shown that macroscopic pathologic assessment of the completeness of the mesorectum of the specimen, scored as complete, partially complete, or incomplete, accurately predicts both local recurrence and distant metastasis.25 Microscopic parameters, such as the status of the circumferential resection margin, the distance between the tumor and nearest circumferential margin (ie, “surgical clearance”), and the distance between the tumor and the closest distal margin, are all important predictors of local recurrence and may be affected by surgical technique. There is strong evidence that the status of the circumferential resection margin is a powerful predictor of local recurrence but is inconsistently evaluated and underreported.25The nonperitonealized surface of the fresh specimen is examined circumferentially, and the completeness of the mesorectum is scored as described in the following.25 The entire specimen is scored according to the worst area.Little bulk to the mesorectumDefects in the mesorectum down to the muscularis propriaAfter transverse sectioning the circumferential margin appears very irregularModerate bulk to the mesorectumIrregularity of the mesorectal surface with defects greater than 5 mm, but none extending to the muscularis propriaNo areas of visibility of the muscularis propria except at the insertion site of the levator ani musclesIntact bulky mesorectum with a smooth surfaceOnly minor irregularities of the mesorectal surfaceNo surface defects greater than 5 mm in depthNo coning toward the distal margin of the specimenAfter transverse sectioning the circumferential margin appears smoothIdentification of MSI-H colorectal tumors is important, as mismatch repair deficiency may serve as a prognostic marker of patient outcome, a predictive marker of response to chemotherapy, and as a screening tool for HNPCC (Lynch syndrome). Revised Bethesda guidelines for HNPCC detection recommend testing colorectal tumors for microsatellite instability under the following circumstances.26Tumor-infiltrating lymphocytes are closely associated with microsatellite instability and medullary architecture (see previous) and should be distinguished from Crohn-like peritumoral infiltrates (lymphoid aggregated or follicles are the tumor edge, not associated with preexisting lymph node).27 Although absolute cut-off values have not been established, only moderate- and high-density intratumoral lymphocytes (approximately 3 or more per high-power field using hematoxylin-eosin–stained sections) should be considered significant.28Other pathologic features associated with MSI-H status in colorectal carcinomas include right-sided location, high-grade histology, and lack of dirty necrosis.28It may be helpful to mark the margin(s) closest to the tumor with ink following close examination of the serosal surface for puckering and other signs of tumor involvement. Margins marked by ink should be designated in the macroscopic description of the surgical pathology report. The serosal surface (visceral peritoneum) does not constitute a surgical margin.In addition to addressing the proximal and distal margins, the circumferential (radial) margin (Figure 3, A through C) must be assessed for any segment either unencased (Figure 3, C) or incompletely encased by peritoneum (Figure 3, B) (see note A). The circumferential margin represents the adventitial soft tissue margin closest to the deepest penetration of tumor (Figure 4) and is created surgically by blunt or sharp dissection of the retroperitoneal or subperitoneal aspect respectively. Multivariate analysis has suggested that tumor involvement of the circumferential margin is the most critical factor in predicting local recurrence in rectal cancer.29 A positive circumferential margin in rectal cancer increases the risk of recurrence by 3.5-fold and doubles the risk of death from disease. For this reason, the circumferential margin should be assessed in all rectal carcinomas as well as colonic segments with nonperitonealized surfaces. The distance between the tumor and radial margin should be reported (see note I). The circumferential margin is considered negative if the tumor is more than 1 mm from the inked nonperitonealized surface but should be recorded as positive if tumor is located 1 mm or less from the nonperitonealized surface because local recurrence rates are similar with clearances of 0 to 1 mm. This includes tumor within a lymph node as well as direct tumor extension, but if circumferential margin positivity is based solely on intranodal tumor, this should be so stated.The mesenteric resection margin is the only relevant circumferential margin in segments completely encased by peritoneum (eg, transverse colon) (Figure 3, A). Involvement of this margin should be reported even if tumor does not penetrate the serosal surface.Sections to evaluate the proximal and distal resection margins can be obtained either by longitudinal sections perpendicular to the margin or by en face sections parallel to the margin. The distance from the tumor edge to the closest resection margin(s) may also be important, particularly for low anterior resections. For these cases, a distal resection margin of 2 cm is considered adequate; for T1 and T2 tumors, 1 cm may be sufficient distal clearance. Anastomotic recurrences are rare when the distance to the closest transverse margin is 5 cm or greater.In cases of carcinoma arising in a background of inflammatory bowel disease, proximal and distal resection margins should be evaluated for dysplasia and active inflammation.In the AJCC system, tumor remaining in a patient after therapy with curative intent (eg, surgical resection for cure) is categorized by a system known as R classification, shown in the following.RX Presence of residual tumor cannot be assessedR0 No residual tumorR1 Microscopic residual tumorR2 Macroscopic residual tumorFor the surgeon, the R classification may be useful to indicate the known or assumed status of the completeness of a surgical excision. For the pathologist, the R classification is relevant to the status of the margins of a surgical resection specimen. That is, tumor involving the resection margin on pathologic examination may be assumed to correspond to residual tumor in the patient and may be classified as macroscopic or microscopic according to the findings at the specimen margin(s).Neoadjuvant chemoradiation therapy in rectal cancer is associated with significant tumor response and downstaging.30 Because eradication of the tumor, as detected by pathologic examination of the resected specimen, is associated with a significantly better prognosis,31 specimens from patients receiving neoadjuvant chemoradiation should be thoroughly sectioned, with careful examination of the tumor site. Minimal residual disease has been shown to have a better prognosis than gross residual disease.31 Although several grading systems for tumor response have been advocated, a 3-point tumor regression grade has been shown to provide good interobserver reproducibility compared with 5-grade schemas and to provide similar prognostic significance.32Tumor regression should be assessed only in the primary tumor; lymph node metastases should not be included in the assessment.Acellular pools of mucin in specimens from patients receiving neoadjuvant therapy are considered to represent completely eradicated tumor and are not used to assign pT stage or counted as positive lymph nodes.Irregular tumor deposits in pericolic or perirectal fat are considered discontinuous extramural extension and are not counted as lymph nodes replaced by tumor. Most examples are because of lymphovascular or, more rarely, perineural invasion.Surgical resection remains the most effective therapy for colorectal carcinoma, and the best estimation of prognosis is derived from the pathologic findings on the resection specimen. The anatomic extent of disease is by far the most important prognostic factor in colorectal cancer.The protocol recommends the TNM staging system of the AJCC and the International Union Against Cancer133 but does not preclude the use of other staging systems.By AJCC/ International Union Against Cancer convention, the designation “T” refers to a primary tumor that has not been previously treated. The symbol “p” refers to the pathologic classification of the TNM, as opposed to the clinical classification, and is based on gross and microscopic examination. pT entails a resection of the primary tumor or biopsy adequate to evaluate the highest pT category, pN entails removal of nodes adequate to validate lymph node metastasis, and pM implies microscopic examination of distant lesions. Clinical classification (cTNM) is usually carried out by the referring physician before treatment during initial evaluation of the patient or when pathologic classification is not possible.For identification of special cases of TNM or pTNM classifications, the “m” suffix and “y” and “r” prefixes are used. Although they do not affect the stage grouping, they indicate cases needing separate analysis.The “m” suffix indicates the presence of multiple primary tumors in a single site and is recorded in parentheses: pT(m)NM.The “y” prefix indicates those cases in which classification is performed during or following initial multimodality therapy (ie, neoadjuvant chemotherapy, radiation therapy, or both chemotherapy and radiation therapy). The cTNM or pTNM category is identified by a “y” prefix. The ycTNM or ypTNM categorizes the extent of tumor actually present at the time of that examination. The “y” categorization is not an estimate of tumor prior to multimodality therapy (ie, before initiation of neoadjuvant therapy).The “r” prefix indicates a recurrent tumor when staged after a documented disease-free interval and is identified by the “r” prefix: rTNM.For colorectal carcinomas, “carcinoma in situ” (pTis) as a staging term includes cancer cells confined within the glandular basement membrane (intraepithelial carcinoma, synonymous with high-grade dysplasia) or invasive into the mucosal lamina propria, up to but not through the muscularis mucosae (intramucosal carcinoma). Tumor extension through the muscularis mucosae into the submucosa is classified as T1 (Figure 5).Direct invasion of other organs or structures includes invasion of other segments of colorectum by way of the serosa or mesocolon, for example, invasion of the sigmoid colon by carcinoma of the cecum is classified as pT4 (Figure 6, A through D). In such a case, both an adjacent organ and the visceral peritoneum are penetrated by tumor. Intramural extension of tumor from 1 subsite (segment) of the large intestine into an adjacent subsite or into the ileum (eg, for a cecal carcinoma) or anal canal (eg, for a rectal carcinoma) does not affect the pT classification.4Tumor that is adherent to other organs or structures macroscopically is classified as T4. However, if no tumor is found within the adhesion microscopically, the tumor should be assigned T3.1For rectal tumors, invasion of the external sphincter is classified as T3, whereas invasion of the levator ani muscle(s) is classified as T4.Tumor in veins or lymphatics does not affect the pT classification.Serosal involvement by tumor cells (pT4a) has been demonstrated by multivariate analysis to have a negative impact on prognosis,34 as does direct invasion of adjacent organs (pT4b). Visceral peritoneal involvement can be missed without thorough sampling and/or sectioning, and malignant cells have been identified in serosal scrapings in as many as 26% of specimens categorized as pT3 by histologic examination alone.34 The absence of standard guidelines for assessing peritoneal involvement may contribute to underdiagnosis.Shepherd and colleagues34 defined the spectrum of microscopic patterns of peritoneal involvement as follows.All the previously listed types of peritoneal involvement were associated with decreased survival, especially types 2 and 3. In contrast, tumor well clear of the serosa had no independent adverse effect on prognosis. Therefore, it is recommended that the T4a category encompass types 2 and 3 of serosal involvement, detailed previously. Free perforation into the peritoneal cavity is always classified as pT4.The regional lymph nodes for the anatomical subsites of the large intestine (Figure 7) are as follows.Nodes along the sigmoid arteries are considered pericolic nodes, and their involvement is classified as N1 or N2 according to the number involved.Perirectal lymph nodes include the mesorectal (paraproctal), lateral sacral, presacral, sacral promontory (Gerota), middle rectal (hemorrhoidal), and inferior rectal (hemorrhoidal) nodes. Metastasis in the external iliac or common iliac nodes is classified as distant metastasis.4All grossly negative or equivocal lymph nodes are to be submitted entirely.14 Grossly positive lymph nodes may be partially submitted for microscopic confirmation of metastasis.Variables affecting number of lymph nodes found in colorectal resection specimens include thoroughness of pathologic examination, surgical procedure performed, variations in immune response,35 and individual patient anatomy. Lymph nodes may be more difficult to identify in specimens from patients who are obese36 or elderly, or after neoadjuvant therapy.37There is no universal agreement on the minimum number of lymph nodes that predict for regional node negativity,38–40 although 12 to 15 lymph nodes has been advocated.14 Removal and pathologic examination of at least 12 lymph nodes from resected colon cancer cases has been proposed by the Commission on Cancer and endorsed by the National Quality Forum as a quality improvement measure; such quality improvement measures are intended to be used for internal monitoring of performance within an organization or group so that analyses and subsequent remedial actions can be taken, as appropriate (see http://www.facs.org/cancer/qualitymeasures.html). If fewer nodes are found, reexamining the specimen for additional lymph nodes, with or without visual enhancement techniques, should be considered.14 The pathology report should clearly state the total number of lymph nodes examined and the total number involved by metastases. Data are insufficient to recommend routine use of tissue levels or special/ancillary techniques.14For microscopic examination of lymph nodes in large resection specimens, lymph nodes must be designated as regional versus nonregional, according to the anatomic location of the tumor. Metastasis to nonregional lymph nodes is classified as distant metastasis and designated as M1.A tumor nodule in the pericolonic/perirectal fat without histologic evidence of residual lymph node tissue is classified in the N category as regional nodal metastasis (lymph node replacement by tumor) if the nodule has the form and smooth contour of a lymph node. If the nodule has an irregular contour, it is recommended that the nodule be classified in the pT category as discontinuous extramural extension.14 Extramural smooth-contour tumor nodules are counted individually as replaced lymph nodes when assigning the pN category.A micrometastasis is defined as tumor measuring greater than 0.2 mm but less than or equal to 2.0 mm in greatest dimension. Micrometastases are classified as N1(mic) or M1(mic) in lymph nodes or at distant sites, respectively. Isolated tumor cells (ITCs) are defined as single tumor cells or small clusters of tumor cells measuring 0.2 mm or less, usually found by special techniques such as immunohistochemical staining, and are classified as N0.4 Because the biologic significance of ITCs (either a single focus in a single node, multiple foci within a single node, or micrometastatic involvement of multiple nodes) remains unproven, N0 is considered justified. The number of lymph nodes involved by micrometastases or ITCs should be clearly stated.Routine assessment of regional lymph nodes is limited to conventional pathologic techniques (gross assessment and histologic examination) and data are currently insufficient to recommend special measures to detect micrometastasis or ITCs. Thus, neither multiple levels of paraffin blocks nor the use of special/ancillary techniques such as immunohistochemistry are recommended for routine examination of regional lymph nodes.14 Specific denotation of the assigned N category is suggested as follows for cases in which ITCs are the only evidence of possible metastatic disease.441pN0 No regional lymph node metastasis histologically, no examination for isolated tumor cells (ITCs)pN0(i−) No regional lymph node metastasis histologically, negative morphologic (any morphologic technique, including hematoxylin-eosin and immunohistochemistry) findings for ITCspN0(i+) No regional lymph node metastasis histologically, positive morphologic (any morphologic technique, including hematoxylin-eosin and immunohistochemistry) findings for ITCspN0(mol−) No regional lymph node metastasis histologically, negative nonmorphologic (molecular) findings for ITCspN0(mol+) No regional lymph node metastasis histologically, positive nonmorphologic (molecular) findings for ITCsPathologic staging is usually performed after surgical resection of the primary tumor. Pathologic staging depends on pathologic documentation of the anatomic extent of disease, whether or not the primary tumor has been completely removed. If a biopsied tumor is not resected for any reason (eg, when technically unfeasible), and if the highest T and N categories or the M1 category of the tumor can be confirmed microscopically, the criteria for pathologic classification and staging have been satisfied without total removal of the primary cancer.Stage 0 Tis N0 M0*Stage I T1 N0 M0 T2 N0 M0Stage IIA T3 N0 M0Stage IIB T4 N0 M0Stage IIIA T1, T2 N1 M0Stage IIIB T3, T4 N1 M0Stage IIIC Any T N2 M0Stage IV Any T Any N M1* M0 is defined as no distant metastasis.1Detection of defects in mismatch repair in colorectal carcinomas is important for detection of Lynch syndrome (a subset of HNPCC syndrome accounting for approximately 2% of all colorectal carcinomas), and examination of the tissue for defective DNA mismatch repair is recommended if any of the criteria in the revised Bethesda guidelines (note J)26 are met. In addition, emerging data suggest that high levels of microsatellite instability in sporadic colon cancers (approximately 15% of all sporadic cases) are associated with better outcome and may serve as a predictor of response to 5-FU–based chemotherapy, although these latter indications for testing are not clearly established and have not been accepted as standard of care.Detection of high levels of microsatellite alterations (MSI) by polymerase chain reaction assay is definitional for defective DNA mismatch repair. This testing is performed on paraffin-embedded tissue and compares results of tumor DNA to that of nonneoplastic tissues from the same patient.Testing for defective DNA mismatch repair may also be performed using immunohistochemistry. The most commonly used methods are immunohistochemistry for MLH1, MSH2, MSH6, and PMS2; antibodies are commercially available. Any positive reaction in the nuclei of tumor cells is considered as intact expression (normal), and it is common for intact staining to be somewhat patchy. An interpretation of expression loss should be made only if positive reaction is seen in internal control cells, such as the nuclei of stromal, inflammatory, or benign epithelial cells. Intact expression of all 4 stains indicates that mismatch repair enzymes tested are intact but does not entirely exclude Lynch syndrome, as approximately 5% of families may have a missense mutation (especially MLH1) that can lead to a nonfunctional protein with retained antigenicity. Defects in lesser-known mismatch repair enzymes may also lead to a similar result, but this situation is rare. Negative results in MLH1 may be due to Lynch syndrome or methylation of the promoter region (as occurs in sporadic MSI colorectal carcinoma). Genetic testing is ultimately required for this distinction, although a specific b-raf mutation is present in many sporadic cases but not familial cancers. Loss of MSH2 expression essentially always implies Lynch syndrome. PMS2 loss is often associated with loss of MLH1 and is only independently meaningful if MLH1 is intact. MSH6 is similarly related to MSH2.