Peritumoral Lymphoid Aggregates Research Articles

Machine Vision–Detected Peritumoral Lymphocytic Aggregates Are Associated With Disease-Free Survival in Patients With Papillary Thyroid Carcinoma

Papillary thyroid carcinoma (PTC) is the most prevalent form of thyroid cancer, with a disease recurrence rate of around 20%. Lymphoid formations, which occur in nonlymphoid tissues during chronic inflammatory, infectious, and immune responses, have been linked with tumor suppression. Lymphoid aggregates potentially enhance the body’s antitumor response, offering an avenue for attracting tumor-infiltrating lymphocytes and fostering their coordination. Increasing evidence highlights the role of lymphoid aggregate density in managing tumor invasion and metastasis, with a favorable impact noted on overall and disease-free survival (DFS) across various cancer types. In this study, we present a machine vision model to predict recurrence in different histologic subtypes of PTC using measurements related to peritumoral lymphoid aggregate density. We demonstrate that quantifying peritumoral lymphocytic presence not only is associated with better prognosis but also, along with tumor-infiltrating lymphocytes within the tumor, adds additional prognostic value in the absence of well-known second mutations including TERT. Annotations of peritumoral lymphoid aggregates on 171 well-differentiated PTCs in the Cancer Genome Atlas Thyroid Carcinoma (TCGA-THCA) data set were used to train a deep-learning model to predict regions of lymphoid aggregates across the entire tissue. The fractional area of the tissue regions covered by these lymphocytes was dichotomized to determine the following 2 risk groups: a significant and low density of peritumoral lymphocytes. DFS prognosticated using these risk groups via the Kaplan-Meier analysis revealed a hazard ratio (HR) of 2.51 (95% CI: 2.36, 2.66), tested on 170 new patients also from the TCGA-THCA data set. The prognostic performance of peritumoral lymphocyte aggregate density was compared against the univariate Kaplan-Meier analysis of DFS using the fractional area of intratumoral lymphocytes within the primary tumor with an HR of 2.04 (95% CI: 1.89, 2.19). Combining the lymphocyte features in and around the tumor yielded a statistically significant improvement in prognostic performance (HR, 3.17 [95% CI: 3.02, 3.32]) on training and were independently evaluated against 62 patients outside TCGA-THCA with an HR of 2.44 (95% CI: 2.19, 2.69). Multivariable Cox regression analysis on the validation set revealed that the density of peritumoral and intratumoral lymphocytes was prognostic independent of histologic subtype with a concordance index of 0.815.

Neurofibroma-like Desmoplastic Melanoma: A Series of Five Cases Exploring the Role of Molecular Testing as a Diagnostic Adjunct and Highlighting the Differential Diagnosis With Diffuse-type Neurofibroma.

A subset of desmoplastic melanomas (DMs) can show extensive morphologic and immunohistochemical overlap with cutaneous diffuse-type neurofibroma. Neurofibroma-like desmoplastic melanoma (NFLDM) thus poses a significant diagnostic pitfall because the clinical implications of these 2 entities differ dramatically. A series of 17 DMs, including 5 cases of NFLDM, were compared with a cohort of 53 cutaneous diffuse-type neurofibromas to explore the utility of molecular testing in the differential diagnosis between NFLDM and neurofibroma and to determine potentially useful morphologic features in this differential diagnosis. Unlike NFLDM, cutaneous diffuse-type neurofibromas: (1) rarely feature intratumoral or peritumoral lymphoid aggregates, (2) consistently harbor an intrinsic stromal support vasculature composed of evenly spaced capillary-sized vessels, and (3) infiltrate adjacent adipose tissue in a dermatofibrosarcoma protuberans-like manner with a complete lack of chronic inflammation or fat necrosis at the leading edge of the tumor. Conversely, DMs, including NFLDM: (1) do not contain Wagner-Meissner bodies, (2) often induce fat necrosis and/or chronic inflammation at the interface with adjacent fibroadipose tissue, (3) lack the intrinsic capillary-sized stromal vasculature observed in most neurofibromas, and (4) may harbor foci of perineuriomatous differentiation, mimicking a hybrid nerve sheath tumor. Any deviation from the expected clinical or morphologic features of cutaneous diffuse-type neurofibroma should raise suspicion for NFLDM. Although not entirely sensitive or specific, molecular testing can help to support the diagnosis of NFLDM by demonstrating genetic abnormalities associated with melanoma, including a UV-light-induced mutational signature, high tumor mutational burden, and/or chromosomal copy number alterations typical of melanoma.

Correlation between stromal Th and Tc lymphocytes and PD-L1 expression in early breast cancer tumors.

Prognostic and predictive value of PD-L1 as a biomarker in breast cancer remains controversial. While some studies suggest its association with negative prognostic parameters, others reported a highly significant association between PD-L1 expression and tumor-infiltrating lymphocytes, which are known to be an independent favorable prognostic factor. The aim of present study is to examine the relationship between immune response markers and PD-L1 expression in early breast cancer. Immunohistochemical expression of PD-L1, along with density and composition of stromal lymphocytic infiltrate and peritumoral lymphoid aggregates was analyzed in 95 samples of invasive breast cancer. A strong positive correlation between PD-L1 expression and the density of stromal lymphocytic infiltrate and peritumoral lymphoid aggregates was identified and a cut-off value of 53% coverage of tumor stroma by lymphocytes, with which PD-L1 positivity can be predicted with excellent diagnostic accuracy, was determined for the first time using statistical methods. Additionally, PD-L1 positivity was observed significantly more often in tumors with higher absolute number of both CD4 and CD8 T-lymphocytes in the stromal infiltrate. No significant correlation with molecular subtype of breast cancer was found. Our results indicate that the density of stromal lymphocytic infiltrate might be a better predictor of PD-L1 positivity in early breast cancer than the molecular subtype and that the key to the optimization of PD-L1 as a biomarker in breast cancer lies in its interpretation in the context of other immune response markers.

Diffuse Intratumoral Stromal Inflammation in Ovarian Clear Cell Carcinoma is Associated With Loss of Mismatch Repair Protein and High PD-L1 Expression.

Ovarian clear cell carcinoma (OCCC) is an aggressive chemotherapy-resistant cancer with limited treatment options, and some OCCCs have mismatch repair (MMR) deficiency (MMRD). Emerging evidence has revealed that various cancers with MMRD are susceptible to anti-programmed death-1/programmed death ligand-1 (anti-PD-1/PD-L1) immunotherapy, and certain histologic features are associated with MMRD. However, few studies have addressed this in OCCC. We reviewed 76 OCCCs for tumor-associated inflammation (intratumoral stromal inflammation and peritumoral lymphocytes) and performed immunohistochemistry for 4 MMR proteins and PD-L1. MMR-deficient OCCCs were analyzed for microsatellite instability (MSI), and those with MLH1 loss were tested for MLH1 promoter methylation. No patients fulfilled the Amsterdam II criteria for the diagnosis of Lynch syndrome. Four (5.3%) tumors showed diffuse intratumoral stromal inflammation obliterating the tumor-stroma interfaces, and none had peritumoral lymphoid aggregates. MMRD was found in 2 (2.6%) tumors; one had MLH1/PMS2 loss (MSI-high and MLH1 promoter methylation was detected) and the other had MSH2/MSH6 loss (MSI-low). Twenty (26.3%) tumors showed tumoral PD-L1 expression ≥1%. Both MMR-deficient tumors showed diffuse intratumoral stromal inflammation and tumoral PD-L1 expression ≥50%. Three of the 4 (75%) tumors with diffuse intratumoral stromal inflammation also showed tumoral PD-L1 expression ≥50%. None of the tumors without diffuse intratumoral stromal inflammation showed MMRD (P=0.021) or tumoral PD-L1 expression ≥50% (P=0.0001). We identified a strong correlation among diffuse intratumoral stromal inflammation, MMRD, and high tumoral PD-L1 expression in a small but significant subset of OCCCs. Histologic evaluation can facilitate patient selection for subsequent anti-PD-1/PD-L1 immunotherapy.

Clinicopathological and molecular features of sporadic colorectal cancers with DNA mismatch repair deficiency: A single center experience

DNA mismatch repair (MMR) proteins may play an important role in colorectal carcinogenesis. In our study, the clinicopathological features of defective MMR in sporadic colorectal adenocarcinomas (CRCs) cases were examined. This is a retrospective study, 457 consecutive cases of colorectal carcinoma with immunohistochemical (IHC) studies for DNA MMR were included.The immunohistochemically (IHC) MMR results of 457 cases were; nuclear expression was intact (proficient, pMMR) in 401 (87.7%) cases and loss of nuclear expression (deficient, dMMR) was found in 56 cases (12.3%). High probability of Lynch syndrome ratio was 2.4% (11/457) in all cases. The loss of PMS2 was predominantly detected in dMMRcases (78.6%). Seventy eight percent of dMMR tumors were located in the proximal colon. In dMMR tumors, prominent peritumoral lymphoid aggregates (LAs) (85.7%) and tumor-infiltrating lymphocytes (TILs) (78.6%) were observed. Among 56 colorectal cancers, we observed expanding /pushing growth pattern in 41 tumors (73.2%), and infiltrative growth pattern in 15 cancers (16.8%). Medullary, mucinous and signet ring cell carcinomas were observed in approximately half of the cases, but there was no statistically significant relationship. Eighty nine percent of dMMR cases had advanced pathologic tumor stage (pT3 or pT4), and this rate was 82.5% in pMMR cases. The average number of positive lymph nodes in cases with dMMR was higher than in pMMR. KRAS mutations were detected in 7.2% (4/13) patients and 14.3% (8/13) patients with MLH1 promoter methylation was observed. Seventy percent of patients with dMMR were alive (n=44) and the mean age of the patients who died was higher. A statistically significant relationship was found between the patients who died and the mean age of surviving patients (p = 0.036). We conclude that the dMMR patients constitutes have a number of distinctive clinicopathological features subtype of sporadic CRC. The overall frequency of defective MMR in colorectal carcinoma cases was found to be Turkish population similar to western studies. dMMR in CRCs were more likely to be of advanced pathologic tumor stage to have a mucinous tumor component and positive LN to show PMS2 loss and to harbour higher numbers of both peritumoral LAs and TILs. They were also more likely to be proximal colon and to occur in male.

"Renal Cell Carcinoma With Leiomyomatous Stroma" Harbor Somatic Mutations of TSC1, TSC2, MTOR, and/or ELOC (TCEB1): Clinicopathologic and Molecular Characterization of 18 Sporadic Tumors Supports a Distinct Entity.

Renal cell carcinoma with (angio) leiomyomatous stroma (RCCLMS) is included as a provisional entity in the 2016 World Health Organization (WHO) classification of renal epithelial neoplasia; however, debate remains whether it represents a distinct entity or a heterogenous group of renal cell carcinomas (RCCs) with overlapping morphology. Also, its relationship to similar tumors occurring in the setting of tuberous sclerosis complex (TSC) is not fully addressed. We analyzed the clinicopathologic, immunohistochemical, and molecular characteristics of 23 sporadic RCCs associated with smooth muscle stroma and classified them into 2 groups, independent of molecular results: (1) RCCLMS (n=18) and (2) clear cell renal cell carcinoma (CCRCC) (n=5). The classification of a case as "RCCLMS" was based on morphologic comparison with 5 "index" RCCs from 3 patients with TSC showing similar features and the presence of diffuse CK7 expression. To investigate mutational and copy number alterations, a 170-gene solid tumor panel was utilized to sequence 14 RCCLMSs and control of 5 CCRCCs. Also, 4 RCCLMSs, suspicious for chromosome 8 monosomy, were further evaluated by a broader 479 gene sequencing panel that included ELOC (also referred to as TCEB1). Clinical information and follow-up data were obtained from electronic medical records. The mean age of patients with RCCLMS was 52 years (range, 33 to 69) with male:female ratio of 1:2. Macroscopically, all tumors were solitary and predominantly (82%) tan/red, circumscribed, and solid. The average tumor size was 2.3 cm (range, 1.1 to 4.5). Microscopically, the distinctive feature included tumor nodules of elongated and frequently branching tubules lined by cells with voluminous clear to mildly eosinophilic cytoplasm (100%), separated by focal to prominent smooth muscle stroma. Additional frequently identified features included: biphasic pattern of collapsed acini surrounding tubules with voluminous cytoplasm (50%), focal papillary architecture (39%), peritumoral lymphoid aggregates (39%), and hemosiderin-laden macrophages (33%). All 11 (100%) RCCLMSs with available staging information were pT1; 78% were WHO/International Society of Urologic Pathology (ISUP) grade 2 and 22% grade 3. Immunophenotypically, RCCLMSs were characterized by diffuse CK7, CAM5.2 and CD10 reactivity (100%). All patients with available follow-up (n=10) were alive and without disease progression after a mean and median follow-up of 25.2 (range: 1 to 58) and 25 months, respectively. The molecular results showed recurrent mutations in all RCCLMS: TSC1 (4), TSC2 (4), MTOR (6), and/or ELOC (2). Five control CCRCCs demonstrated primary alterations in VHL gene, while all 14 RCCLMS cases tested had intact VHL gene. Of 2 RCCLMSs with confirmed monosomy 8, 1 showed a hotspot ELOC mutation without TSC/MTOR mutations, and 1 showed a previously undescribed 3-bp in-frame ELOC deletion, along with a truncating TSC1 mutation. In conclusion, RCCLMS, as defined herein, harbors recurrent mutations of TSC1/TSC2, MTOR, and/or ELOC, consistent with hyperactive MTOR complex. Our findings argue that these tumors represent the sporadic counterpart to morphologically identical tumors occurring in TSC patients. Finally, the data support that RCCLMS is a novel subtype of RCC with unique morphologic, immunohistochemical, and molecular characteristics that is distinct from CCRCC and clear cell-papillary RCC.

Loss of ARID1A expression is associated with DNA mismatch repair protein deficiency and favorable prognosis in advanced stage surgically resected esophageal adenocarcinoma

Esophageal adenocarcinoma often presents at an advanced stage and has a dismal prognosis. Current prognostic markers have limited utility. ARID1A is implicated as a tumor suppressor gene in esophageal adenocarcinoma. Loss of ARID1A expression correlates with DNA mismatch repair (MMR) protein deficiency in other tumors. We hypothesized that ARID1A loss is associated with prognosis and DNA MMR protein deficiency in esophageal adenocarcinoma. Tissue microarrays representing 316 surgically resected esophageal adenocarcinomas without neoadjuvant treatment were evaluated for ARID1A and MMR proteins by immunohistochemistry. Loss of ARID1A expression (ARID1A-loss) was detected in 41 of 316 (13%) adenocarcinomas. MMR deficiency was identified in 5% (17/316) but was detected more frequently in ARID1A-loss adenocarcinomas (13/41, 32%) than in ARID1A-retained adenocarcinomas (4/275, 1%; P < .001). Morphologically, ARID1A-loss adenocarcinomas frequently demonstrated peritumoral lymphoid aggregates (90%) and tumor infiltrating lymphocytes (51%). In patients with locally advanced or metastatic disease (stages III or IV, N = 169), patients with ARID1A-loss adenocarcinomas (N = 22) had longer overall survival than patients with ARID1A-retained adenocarcinomas (median [month]: 26 vs. 16, P = .010). In these patients, ARID1A-loss correlated with a 56% reduction in mortality independent of other prognostic factors (P = .007). In summary, loss of ARID1A expression is associated with DNA MMR protein deficiency in esophageal adenocarcinoma. Furthermore, ARID1A loss is independently associated with a more favorable prognosis for patients with locally advanced or metastatic esophageal adenocarcinomas.

The Crohn's-Like Lymphoid Reaction to Colorectal Cancer-Tertiary Lymphoid Structures With Immunologic and Potentially Therapeutic Relevance in Colorectal Cancer.

The Crohn's-like lymphoid reaction (CLR) to colorectal cancer (CRC), a CRC-specific ectopic lymphoid reaction, is thought to play an important role in the host response to CRC. CLR is characterized by peritumoral lymphocytic aggregates that are found at the advancing edge of the tumor. Spatial and molecular characterization of CLR within the tumor microenvironment (TME) have uncovered a spectrum of peritumoral lymphoid aggregates with varying levels of organization and maturation. In early stages of CLR development, CD4+ T-cells cluster predominantly with mature antigen presenting dendritic cells. As CLR matures, increasing numbers of B-cells, as well as follicular dendritic cells are recruited to create lymphoid follicles. When highly organized, CLR resembles functional tertiary lymphoid structures (TLS), allowing for lymphocyte recruitment to the TME and promoting a tumor-specific adaptive immune response. CLR has been consistently associated with favorable prognostic factors and improved survival among CRC patients, often providing more prognostic information than current clinical staging systems. However, consensus is lacking regarding CLR scoring and it is not clinically assessed or reported. Differences between CLR and other cancer-associated lymphoid structures exist both in primary and metastatic disease, underscoring the need to characterize organ-specific TLS. Further research is needed to explore the role of CLR in predicting response to immunotherapy and to leverage CLR to promote immunotherapeutic strategies in CRC.

Crohn's-Like Lymphoid Reaction is Associated with Oncological Prognosis and Nutritional Status in Patients with Pathological Stage II/III Gastric Cancer.

Peritumoral lymphoid aggregates, termed Crohn's-like lymphoid reaction (CLR), are markers of an antitumor immune response, which is an important predictor of patient outcome. In this study, we investigated the prognostic utility of CLR and its relationship with nutritional status in patients with gastric cancer (GC). The study included 170 patients who underwent curative surgery for pathological stage (pStage) II/III GC. The maximum diameters of peritumoral and normal mucosal CLR aggregates were measured, and the median peritumoral diameter (0.57mm) was used to stratify patients into two groups (large-CLR and small-CLR). The relationships between CLR size and preoperative nutritional status (body mass index, body composition status, Onodera's prognostic nutritional index), tumor-infiltrating CD8+ T-lymphocyte count, and survival were evaluated. Peritumoral CLR aggregates were significantly larger than aggregates in the normal mucosa. Clinicopathological variables were not significantly different between the two patient groups; however, the large-CLR group had better cancer-specific survival (p=0.018) and recurrence-free survival (p=0.03) than the small-CLR group. Multivariate analysis revealed that CLR size was an independent prognostic factor for cancer-specific survival [hazard ratio (HR) 2.13, 95% confidence interval (CI) 1.3-3.56, p=0.002] and recurrence-free survival (HR 1.96, 95% CI 1.22-3.19, p=0.005). Nutritional status markers were significantly poorer for the small-CLR group than the large-CLR group. CD8+ T-cell tumor infiltration was positively correlated with CLR size but not with patient survival. CLR size correlated with patient nutritional status and prognosis and may be helpful in identifying high-risk populations of pStage II/III GC patients.

Colorectal large-cell neuroendocrine carcinoma with lymphoid stroma: further evidence confirming a unique subtype associated with MLH1/PMS2 loss, BRAF mutation, Epstein-Barr virus negativity, and the possibility of a better prognosis.

Pure large-cell neuroendocrine carcinoma (LCNEC) is an uncommon but well-recognised primary tumour of the colorectum. It is characterised by large cells organised in a discernible neuroendocrine pattern with >20 mitoses per 10 high-power fields (HPFs), and/or a Ki67 index of >20%, and coagulative tumour necrosis is invariably present. These features are supplemented by positivity for neuroendocrine immunohistochemical markers. The aim of this study was to highlight three primary LCNECs of the colorectum. All three patients were elderly females, aged 79, 85 and 89years, who presented with ascending colon (two) tumours and a rectal tumour. All three tumours were large, ulcerated, polypoid masses (85, 76 and 55mm; average size 72mm) and were pT3N2. Histologically, the tumours were composed of packets and nests of cells with rosettes; other areas were in sheets composed of large cells. The mitotic counts were 23/10 HPFs, 27/10 HPFs and 24/10 HPFs, respectively. There was no mucosal dysplasia, precursor adenoma or associated adenocarcinoma component. All cases contained mainly peritumoral lymphoid aggregates, with smaller numbers of intratumoral lymphocytes. Synaptophysin, chromogranin (less intensely) and epithelial markers were expressed in all cases in the majority of the tumour cells. The Ki67 proliferative indices were 95%, 100%, and 80%, respectively. Two patients survived for 48 and 72months, whereas the third is alive after 12months without evidence of recurrence. These unusual primary colorectal LCNECs with an accompanying lymphoid component are characterised by loss of MLH1/PMS2, BRAF mutation, microsatellite instability, and Epstein-Barr virus negativity. The patients also have better overall survival than those with LCNECs lacking an accompanying lymphoid component.

Giant cellular neurilemmoma, a rare mesenchymal tumor of the oesophagus: A case report

Introduction: Gastrointestinal schwannomas are classified as mesenchymal or neuroectodermal neoplasms. Most common site is stomach followed by rectum. Schwannoma of oesophagus is very rare. It can present with dysphagia and odynophagia. Case Report: A 30­year­old female was presented with progressive dysphagia, mild odynophagia, retrosternal heartburn and vomiting for last six months. On radiological investigations a rounded radio opaque shadow in right paratracheal region was seen. Endoscopy showed ulcerated mucosa that bled on touch. Lumen was narrowed. Endoscopic biopsy showed only mild dysplasia in squamous epithelial lining. Segmental oesophagectomy was done to remove the mass. On gross examination an already cut open segment of oesophagus of about 6 cm in length was received. An irregular, lobulated, firm, grey white growth, of 7x5x8.5 cm, having smooth external surface was observed towards serosal surface. Cut surface was homogenous white. Histology showed monomorphic spindle shaped cells arranged in fascicular and whorled pattern with nuclear palisading at places. Peri tumoral lymphoid aggregates were also seen. Conclusion: Oesophageal schwannomas are benign tumors having excellent prognosis following surgical resection. A case of oesophageal schwannoma is documented here.

Objective Criteria for Crohn-like Lymphoid Reaction in Colorectal Cancer

We aimed to determine semiquantitative evaluation criteria for Crohn-like lymphoid reaction (CLR). We reviewed 1,032 patients with colorectal cancer and evaluated CLR by counting all peritumoral lymphoid aggregates (LAs) and by measuring the maximum diameter of the largest LA. The maximum diameter of the largest LA, rather than the number, had a significant impact on survival. Active CLR determined by the 1-mm rule was significantly associated with MLH1/MSH2 immunohistochemical staining deficiency. The group with LAs 1 mm or larger had lower recurrence (P = .0008) and a higher survival rate (P < .0001) than that without LAs 1 mm or larger. These results were similarly observed in another cohort of 500 patients with colorectal cancer. The k values for CLR evaluation among 8 observers were 0.67 for the 1-mm rule and 0.50 for Graham's criteria. The size of the largest LA best reflects the specific characteristics of CLR, and the 1-mm rule is expected to improve assessment reproducibility.

Calcifying Fibrous Tumor of the Stomach: Clinicopathologic and Molecular Study of Seven Cases With Literature Review and Reappraisal of Histogenesis

Calcifying fibrous tumor (CFT) is a rare benign mesenchymal tumor composed of hyalinized fibrous tissue with interspersed bland fibroblastic spindled cells, scattered psammomatous, and/or dystrophic calcifications and variably prominent mononuclear inflammatory infiltrate. CFTs show a predilection for the abdominal cavity and soft tissue. To date, 6 gastric and 3 intestinal CFTs have been reported. We analyzed 7 gastric CFTs including 6 new cases. Patients were 4 men and 3 women with a mean age of 53 years (range, 40 to 77). Mean tumor size was 2.2 cm. Most tumors originated in the gastric body (6/7). Six were incidental findings at autopsy or during surgery for other diseases. One ulcerated tumor caused iron deficiency anemia and ulcer symptoms. Six tumors involved the muscularis propria with variable submucosal and subserosal extension and 1 arose within thickened muscularis mucosae adjacent to a mucosal invagination. Histology was typical with uniformly hypocellular vaguely storiform collagen, lymphoplasmacytic infiltrates, lymphoid aggregates and psammomatous, and dystrophic calcifications. Peritumoral lymphoid aggregates were seen in 3 cases. Adjacent muscle coat contained lymphoid aggregates with fiber degeneration (2), minute CFT-like foci (1), and calcifications (1). In none of the cases were there remnants of burnt-out GIST, inflammatory fibroid polyp, inflammatory myofibroblastic tumor, leiomyoma, schwannoma, or other specific lesion. All tumors were negative for CD117, S100, smooth muscle actin, desmin, ALK1, h-caldesmon, and PDGFRA. Two stained focally with CD34. Scattered IgG4-positive plasma cells were seen in 4 of 6 cases stained with this marker. All 5 tumors with available tissue for molecular analysis were wild-type for KIT and PDGFRA. Three patients had follow-up (range, 12 to 24 mo); none developed recurrence. Gastric CFTs are distinct from sclerosing GIST and other mesenchymal gut lesions and may represent a localized inflammatory fibrosclerosis in response to immune-mediated or other-type tissue injury affecting the muscularis propria. They differ from soft tissue CFTs by smaller size, older age at presentation and lack of recurrence, and from peritoneal CFTs by equal gender distribution, older age, and absent multifocal occurrence.

Feline vaccine-associated fibrosarcoma: morphologic distinctions.

Forty-four primary feline vaccine-associated fibrosarcomas and 16 recurrences were examined histologically for detailed morphologic characterization with emphasis on tumor grade, presence of neoplastic multinucleated giant cells, presence and proportion of T and B lymphocytes within the tumor, and thin and intermediate filament contents of neoplastic and stromal cells. The microvascularity and proliferation rates of central and peripheral areas of the tumors were also quantified by computerized image analysis. For primary fibrosarcomas, 11 of 44 (25%) were grade I, 21 of 44 (47.7%) were grade II, and 12 of 44 (27.3%) were grade III. The recurrences followed a similar pattern: 4 of 16 (25%) were grade I, 8 of 16 (50%) were grade II, and 4 of 16 (25%) were grade III. A positive correlation was found between the presence of neoplastic multinucleated giant cells and tumor grade. These cells were present in 9 of 12 (75%) of grade III and none of the grade I tumors. Prominent peritumoral lymphoid aggregates or follicles were present in 59% of the tumors, and many contained high proportions of T lymphocytes, varying from 19 to 87%. All fibrosarcomas were immunoreactive for vimentin and 28 of 44 (64%) were reactive for alpha-smooth muscle actin. The actin-positive cells were either part of the tumor or formed a capsule around tumor nodules. The peripheral vascularity was significantly higher than the central vascular density but no difference was found in tumor cell proliferation rates between the two areas. Centrally located, fluid-filled micro- or macrocavitations were frequently observed in the large vaccine sarcomas and probably formed secondary to rapid tumor growth and central necrosis.