Anal Tumors Research Articles

[Translated article] Retrospective Study of Risk Markers for Developing High-Grade Anal Intraepithelial Neoplasm in Men Who Have Sex With Men Living With HIV

BackgroundHigh-grade anal intraepithelial squamous lesion is significantly prevalent among men who have sex with men and are infected with the human immunodeficiency virus (HIV). This condition—the precursor to anal cancer—significantly increases the risk of developing it. Conversely, low-grade anal intraepithelial squamous typically follow a benign course and usually regress spontaneously. Materials and methodsTo describe a population of men who have sex with men living with HIV followed in a specialized anal cancer screening unit we conducted an observational, retrospective, and single-center study. ResultsNinety-four patients were analyzed, with a mean age of 39±9 years, and a 87% positivity rate for high-risk human papillomavirus (HR-HPV). At the initial visit, 47% presented with low-grade squamous intraepithelial lesions. The progression rate to high-grade squamous intraepithelial lesion was 37.2 per 100,000 patients/year. None of the patients developed anal cancer. Tobacco and alcohol consumption were associated with this progression. DiscussionIn this series, longer duration of HIV infection, tobacco and alcohol use and the presence of HR-HPV were significantly associated with the occurrence of high-grade intraepithelial lesions. A lower risk of progression was seen in patients with higher education. ConclusionIn men who have sex with men living with HIV, the association of factors such as smoking, alcohol, the presence of HR-HPV and an increased burden of human papillomavirus disease makes these patients more susceptible to develop high-grade anal squamous lesions.

Anal carcinoma - exploring the epidemiology, risk factors, pathophysiology, diagnosis, and treatment.

Anal carcinoma is a relatively rare tumor that accounts for approximately 2% of gastrointestinal malignancies and less than 7% of anorectal cancers. Most anal tumors originate between the anorectal junction and the anal verge. Risk factors for the disease include human papillomavirus infection, human immunodeficiency virus, tobacco use, immunosuppression, female sex, and older age. The pathogenesis of anal carcinoma is believed to be linked to human papillomavirus-related inflammation, leading to dysplasia and progression to cancer. Squamous cell carcinoma is the most common type of anal tumor, with an annual incidence of approximately 1 to 2 per 100000 persons. Treatment regarding anal cancer has emerged over time. However, chemoradiation therapy remains the mainstay approach for early localized disease. Patients with metastatic disease are treated with systemic therapy, and salvage surgery is reserved for disease recurrence following chemoradiation. This article aims to provide background information on the epidemiology, risk factors, pathology, diagnosis, and current trends in the management of anal cancer. Future directions are briefly discussed.

Invasive cancer and spontaneous regression two weeks after papillomavirus infection.

AbstractDevelopment of invasive cancer in mammals is thought to require months or years after initial events such as mutation or viral infection. Rarely, invasive cancers regress spontaneously. We show that cancers can develop and regress on a timescale of weeks, not months or years. Invasive squamous cell carcinomas developed in normal adult, immune-competent mice as soon as 2 weeks after infection with mouse papillomavirus MmuPV1. Tumor development, regression or persistence was tissue- and strain-dependent. Cancers in infected mice developed rapidly at sites also prone to papillomavirus-induced tumors and cancers in humans – the throat, anus, and skin – and their frequency was increased in mice constitutively expressing the papillomavirus E5 oncogene, which MmuPV1 lacks. Cancers and dysplasia in the throat and anus regressed completely within 4-8 weeks of infection; however, skin lesions in the ear persisted. T-cell depletion in the mouse showed that regression of throat and anal tumors requires T cells. We conclude that papillomavirus infection suffices for rapid onset of invasive cancer, and persistence of lesions depends on factors including tissue type and host immunity. The speed of these events should promote rapid progress in the study of viral cancer development, persistence, and regression.Summary Graphic

Topical Protease Inhibitor Increases Tumor-Free and Overall Survival in CD4-Depleted Mouse Model of Anal Cancer.

Patients with immunodeficiencies and older age are at an increased risk of anal cancer. Transgenic K14E6/E7 mice with established high-grade anal dysplasia were treated topically at the anus with the protease inhibitor saquinavir (SQV) in the setting of CD4+ T-cell depletion to mimic immunodeficiency. To ensure tumor development, specific groups were treated with a topical carcinogen (7,12-Dimethylbenz[a]anthracene (DMBA)). The treatment groups included the vehicle (control), DMBA only, topical SQV, and topical SQV with DMBA, as well as the same four groups with CD4 depletion. The mice were monitored weekly for tumor development. Upon reaching 20 weeks of treatment, the mice were sacrificed, and their anal tissue was harvested for histological analysis. None of the mice in the SQV or control groups developed overt anal tumors, except three mice that were CD4-depleted. The CD4-depleted mice treated with DMBA had significantly increased tumor-free survival and overall survival as well as decreased tumor-volume growth over time when treated with SQV. These data suggest that topical SQV, in the setting of CD4 depletion and high-grade anal dysplasia, can increase tumor-free and overall survival; thus, it may represent a viable topical therapy to decrease the risk of progression of anal dysplasia to anal cancer.

Role of dynamic ctDNA monitoring in cervical and anal epidermoid carcinomas under curative chemoradiation.

3141 Background: Cervical and anal canal squamous cell carcinoma (SSC) are a significant health problem in underdevelopment countries. Definitive chemoradiation (CRT) is the standard-of-care (SOC) approach for curative treatment in locally advanced disease. Due to the common substantial local inflammation during CRT, the conventional clinical image cannot identify non-responders early. In this scenario, the evaluation of circulating tumor DNA (ctDNA) is a promising tool for real-time tumor response monitoring. Methods: We performed a prospective multicentric cohort study of patients treated between 2020 and 2023 in tertiary oncologic centers in Brazil to evaluate the role of ctDNA dynamic monitoring in epidermoid cervical (CC) and anal cancer (AC) T1-4, N0-1, M0 by AJCC 8th edition and candidates to complete curative CRT. The cDNA was assessed by Signatera test at D1, D29, immediately post-treatment, 8 weeks (w) post-CRT, 24w post-CRT, every 6 months (m) in the first 1-2 years(y), and yearly at 3-5y of follow-up (FUP). The primary endpoint was to estimate the correlation of ctDNA with a tumoral response assessed by conventional routine image and clinical evaluation at 8w. Secondary endpoints included a correlation between ctDNA results at different time points with progression-free survival (PFS) and overall survival (OS). The predictive potential of the biomarker was evaluated using receiving operating characteristic (ROC) curve analysis. Results: We included 33 patients, and 27 were evaluable with ctDNA, with a median FUP of 10m. The majority were female (n=23, 85.1%), and 3 (11%) were HIV-positive(+). Most patients presented with positive nodes and stage III disease (n=18, 66.6%). In the AC group (n=15), the majority received CRT with capecitabine and cisplatin (n=12, 55.5%); in the CC group (n=12), all pts received cisplatin. All pts tested expressed ctDNA+ before treatment. At 8w, images had a sensitivity of 42.8% and specificity of 100% for disease progression (area under the curve [AUC] 0.714), while ctDNA yielded a sensitivity of 85.7% and specificity of 89.4% (AUC 0.875). The ctDNA+ immediately after CRT ended (32%) was consistent with ctDNA+ at 8w (30.7%) and 24w (30%). Pts with ctDNA+ immediately post CRT have a higher risk of disease progression with PFS of 8.2m in ctDNA+ and not reached in ctDNA- group (HR:17.5; IC95%:1.9-157.3; p=0.01). Data are immature for OS analysis. Conclusions: CtDNA immediately post-CRT has a high predictive value in patients with anal and cervical tumors in early access CRT non-responders, who are at a high risk of disease progression. This biomarker should be considered for tailoring strategies of treatment escalation in this population.

Multimode ultrasound imaging of an anal canal gastrointestinal stromal tumour (GIST).

Gastrointestinal stromal tumours (GISTs) can develop throughout the entire gastrointestinal tract, but these tumours are usually found in the stomach and small intestine. In this case, a rare GIST arising from the anal canal was investigated using high-frequency endoanal ultrasound and external three-dimensional ultrasound with tomographic ultrasound imaging. The endoanal approach revealed the inner structure of the tumour. External ultrasound was used to determine the relationship between the lesion and surrounding tissues. In the limited reports of anal canal GISTs, no other lesions have been correctly diagnosed preoperatively or displayed in detail on imaging. The multilayer structure of the anal sphincter and these lesions can be clearly displayed by a variety of ultrasound imaging methods, which are nonradiative, low-cost and easily accessible.Modern ultrasound has the potential for broad application in anal canal tumour diagnosis and surveillance.

Radiotherapy for Canine Apocrine Gland Anal Sac Adenocarcinoma: Survival Outcomes and Side Effects of a Palliative Treatment Protocol of 20 Gy in Five Consecutive Fractions.

This research aims to evaluate the outcomes of a radiotherapy protocol, consisting of five fractions of 4 Gy each, resulting in a total dose of 20 Gy for apocrine gland anal sac tumors and local lymph nodes in canines. This protocol was assessed as a palliative treatment for macroscopic tumors alone, or in combination with additional therapies under different scenarios. Medical records from fifty canine patients met the inclusion criteria and were divided into different treatment groups: radiotherapy alone (n = 22, 44%), radiotherapy with chemotherapy or targeted therapy with toceranib (n = 18, 36%), surgery with radiotherapy (n = 5, 10%), and surgery with radiotherapy and chemotherapy or targeted therapy with toceranib (n = 5, 10%). Patients who received radiotherapy alone had a median survival time of 384 days (95% CI 198-569) and 628 days (95% CI 579-676) for RT + additional therapies. The median time to progression for patients with radiotherapy alone was 337 days (95% CI 282-391 days), and 402 days (95% CI 286-517 days) for radiotherapy plus additional treatments. Acute side effects were mild, with the majority having diarrhea (61%), and only one patient developed grade III late effects VRTOG v2 classification; however, this happened 22 months after the first radiotherapy protocol after re-irradiation. The results demonstrate that radiotherapy alone under this protocol provided a comparable median time to progression vs. radiotherapy plus additional treatments while maintaining acceptable side effects. The combination of this protocol with other treatment modalities offers attractive results for local disease control and survival while maintaining acceptable toxicities. Overall, these findings contribute to the growing evidence supporting the role of radiotherapy in managing apocrine gland anal sac adenocarcinoma in dogs.

Significance of lateral lymph node dissection in squamous cell carcinoma of the anal canal: a retrospective cohort study.

The JCOG (Japan Clinical Oncology Group) 0212 study did not confirm the noninferiority of mesorectal excision (ME) alone to ME with LLND for rectal or anal adenocarcinomas. Furthermore, the significance of LLND for SCCs remains unknown. We evaluated the significance of lateral lymph node dissection (LLND) of squamous cell carcinoma (SCC) of the anal canal. This retrospective cohort study was conducted in 435 patients with SCCs among 1,781 patients with anal canal tumors. In 40 patients who underwent LLND, the 5-year relapse-free survival (5y-RFS) and 5-year overall survival (5y-OS) were compared between groups with positive and negative histopathological findings. In 71 patients with negative lateral lymph node metastasis in the preoperative diagnosis, the 5y-RFS, 5y-OS, and 5-year local recurrence-free survival were compared between patients who did and did not undergo LLND. The clinical and pathological T stages predicted pathological lateral pelvic lymph node metastasis. There was no statistically significant difference in 5y-RFS and 5y-OS between patients who did and did not undergo LLND. Among patients who underwent LLND, 5y-RFS in those with positive histopathological findings (15.0%) was worse than that in those without (59.2%) (p = 0.002). In patients who underwent LLND, 5y-RFS in those with positive histopathological findings than in those without LLND did not contribute to prognosis.

Current update on the role of endoanal ultrasound: a primer for radiologists.

Endoanal ultrasound (EAUS) is a valuable imaging modality for the evaluation of anal and perianal pathologies. It provides detailed information about the anatomy and physiology of the anorectal region and has been used in pre-and post-operative settings of anorectal pathologies. EAUS is not only useful in the evaluation of benign pathologies but also in loco-regional staging of anal and rectal tumors. EAUS has several advantages over MRI, including reduced cost, better patient tolerance, and improved scope of application in patients with contraindications to MRI. Despite its benefits, EAUS is not widely performed in many centers across the globe. This article aims to educate radiologists, trainees, and surgeons about the indications, contraindications, patient preparation, imaging technique, and findings of EAUS. We will also highlight the technical difficulties, diagnostic challenges, and procedural complications encountered during EAUS, along with a comparative analysis of EAUS with other imaging approaches.

Hospitalization burden associated with anus and penis neoplasm in Spain (2016-2020)

ABSTRACT In 2020, there were approximately 50,865 anal cancer cases and 36,068 penile cancer cases worldwide. HPV is considered the main causal agent for the development of anal cancer and one of the causal agents responsible for the development of penile cancer. The aim of this epidemiological, descriptive, retrospective study was to describe the burden of hospitalization associated with anal neoplasms in men and women and with penis neoplasms in men in Spain from 2016 to 2020. The National Hospital Data Surveillance System of the Ministry of Health, Conjunto Mínimo Básico de Datos, provided the discharge information used in this observational retrospective analysis. A total of 3,542 hospitalizations due to anal cancer and 4,270 hospitalizations due to penile cancer were found; For anal cancer, 57.4% of the hospitalizations occurred in men, and these hospitalizations were also associated with significantly younger mean age, longer hospital stays and greater costs than those in women. HIV was diagnosed in 11.19% of the patients with anal cancer and 1.74% of the patients with penile cancer. The hospitalization rate was 2.07 for men and 1.45 for women per 100,000 in anal cancer and of 4.38 per 100,000 men in penile cancer. The mortality rate was 0.21 for men and 0.12 for women per 100,000 in anal cancer and 0.31 per 100.000 men in penile cancer and the case-fatality rate was 10.07% in men and 8,26% in women for anal cancer and 7.04% in penile cancer. HIV diagnosis significantly increased the cost of hospitalization. For all the studied diagnoses, the median length of hospital stays and hospitalization cost increased with age. Our study offers relevant data on the burden of hospitalization for anal and penile cancer in Spain. This information can be useful for future assessment on the impact of preventive measures, such as screening or vaccination in Spain.

Nodal Elective Volume Selection and Definition during Radiation Therapy for Early Stage (T1-T2 N0 M0) Perianal Squamous Cell Carcinoma: A Narrative Clinical Review and Critical Appraisal.

Distinction between anal canal and perianal squamous cell carcinomas (pSCCs) is essential, as these two subgroups have different anatomical, histological, and lymphatic drainage features. Early-stage true perianal tumors are very uncommon and have been rarely included in clinical trials. Perianal skin cancers and aCCs are included in the same tumor classification, even though they have different lymphatic drainage features. Furthermore, pSCCs are treated similarly to carcinomas originating from the anal canal. Radiation therapy (RT) is an essential treatment for anal canal tumors. Guidelines do not differentiate between treatment volumes for perianal tumors and anal cancers. So far, in pSCC, no study has considered modulating treatment volume selection according to the stage of the disease. We conducted a narrative literature review to describe the sites at higher risk for microscopic disease in patients with early-stage perianal cancers (T1-T2 N0 M0) to propose a well-thought selection of RT elective volumes.

Preclinical Models of Anal Cancer Combined-Modality Therapy

IntroductionThere have been no significant changes in anal cancer treatment options in 4 decades. In this study, we highlight two preclinical models designed to assess anal cancer treatments. Materials and methodsTransgenic K14E6/E7 mice were treated with 7, 12-dimethylbenz(a)anthracene until anal tumors developed. Mice were treated with localized radiation in addition to chemotherapy (combined-modality therapy [CMT]) and compared to no treatment control (NTC). K14E6/E7 mouse anal spheroids with and without Pik3ca mutations were isolated and treated with vehicle, LY3023414 (LY3) (a drug previously shown to be effective in cancer prevention), CMT, or CMT + LY3. ResultsIn the in vivo model, there was a significant increase in survival in the CMT group compared to the NTC group (P = 0.0392). In the ex vivo model, there was a significant decrease in the mean diameter of CMT and CMT + LY3-treated spheroids compared to vehicle (P ≤ 0.0001). For LY3 alone compared to vehicle, there was a statistically significant decrease in spheroid size in the K14E6/E7 group without mutation (P = 0.0004). ConclusionsWe have provided proof of concept for two preclinical anal cancer treatment models that allow for the future testing of novel therapies for anal cancer.

Low Anterior Resection Syndrome (LARS) after Surgery for Rectal Cancer: An Inevitable Price to Pay for Survival, or a Preventable Complication?

Rectal cancer is frequent and often treated with sphincter-saving procedures that may cause LARS, a syndrome characterized by symptoms of bowel disfunction that may severely affect quality of life. LARS is common, but its pathogenesis is mostly unknown. The aim of this study is to assess the incidence of LARS and to identify potential risk factors. We performed an observational retrospective single center analysis. The following data were collected and analyzed for each patient: demographics, tumor-related data, and intra- and peri-operative data. Statistical analysis was conducted, including descriptive statistics and multivariate logistic regression to identify independent risk factors. Total LARS incidence was 31%. Statistically significant differences were found in tumor distance from anal verge, tumor extension (pT and diameter) and tumor grading (G). Multivariate analysis identified tumor distance from anal verge and tumor extension as an independent predictive factor for both major and total LARS. Adjuvant therapy, although not significant at univariate analysis, was identified as an independent predictive factor. Time to stoma closure within 10 weeks seems to reduce incidence of major LARS. bold LARS affects a considerable portion of patients. This study identified potential predictive factors that could be useful to identify high risk patients for LARS.

Prognostic impact of post-treatment FDG PET/CT in anal canal cancer: A prospective study

Background and purposeThe aim of our prospective study was to assess the prognostic value of 18F-FDG PET/CT performed two months post treatment for anal canal neoplasm. Population and methodsConsecutive patients with histologically proved anal cancer, with 18F-FDG PET/CT pre and two months post treatment were included. Patients were not previously treated for this neoplasm and then received radiotherapy ± chemotherapy. Clinical and pathologic data were collected and for 18F-FDG PET/CT visual and quantitative analysis (standardized uptake value, metabolic volume) were performed; response was classified according to EORTC and PERCIST criteria. The results were assessed for disease free survival and local recurrence free survival using the log-Rank test ResultsFrom December 2014 to September 2019, 94 consecutive patients were screened and 78 were included in this study. Median follow-up was 51 months. Two months post treatment, 37 patients (47.4%) had a complete radiological response according to both EORTC and PERCIST criteria, 66 patients (84.6%) had a clinical complete response. For disease free survival, the prognostic value of complete response was statistically significant (p=0.02) with 18F-FDG PET/CT and with clinical examination (p<0.001). For local recurrence free survival, the prognostic value with 18F-FDG PET/CT was lower (p=0.04) than clinical examination (p < 0.007). ConclusionWhile clinical examination remains the gold standard for post treatment evaluation in anal cancer, 18F-FDG PET/CT has a statistically significant prognostic value. These two assessments could be combined to improve early evaluation.

Hepatic Metastasectomy in Squamous Cell Carcinoma of the Anal Canal: A Case Series of a Curative Approach.

Squamous cell carcinoma of the anal canal (SCCA) is rare. Most cases are diagnosed in a localized setting. Metastatic SCCA is rare, and investigation has been limited in the past for these patients. We believe that hepatic-only metastatic disease could have a unique treatment landscape compared to diseases with diffuse metastatic involvement. Here, we describe cases at our institution. We reviewed eight SCCA cases with hepatic-only metastatic disease (diagnosed February 2018-January 2022). The objectives were to determine the overall survival and disease-free survival with this approach. The median age was 62 years old (yo). Patients had an ECOG of 0-1. All patients received definitive chemoradiation to their primary anal tumor. A median of three months of neoadjuvant systemic therapy was provided. All patients had a response on their first scan after systemic therapy. Sixty-two percent received carboplatin + paclitaxel. A complete pathologic response was seen in 62% of patients. At their last follow-up, all patients were alive. Three patients had recurrent disease. The estimated 1-year disease-free survival probability was 56.2%. Our report shows the feasibility of a curative-intent approach for patients with hepatic-only metastatic SCCA following the neoadjuvant application of carboplatin + paclitaxel. This approach appears promising in these select patients and warrants further investigation.

Regional transarterial chemoembolization combined with chemoradiotherapy for locally advanced rectal cancer: a retrospective study of a new combination.

Locally advanced rectal cancer (LARC) has a high risk of distant metastasis (DM). Currently, many treatment courses of LARC have arisen, but patients' DM status has not significantly improved. This study was designed to compare the effect between preoperative regional transarterial chemoembolization combined with neoadjuvant chemoradiotherapy and standard neoadjuvant therapy on preventing DM in patients with LARC. A total of 81 LARC patients between July 2013 and May 2018 were enrolled in this retrospective study. Among them, 44 patients received preoperative regional transarterial chemoembolization combined with concurrent chemoradiotherapy (the interventional group), and 37 patients received only neoadjuvant chemoradiotherapy (the control group). The baseline data; preoperative toxicities; postoperative DM rate within 1, 2, and 3 years; and postoperative complications were compared between the two groups. All patients successfully completed their treatments. There were no significant differences between the two groups in age, gender, tumor size, distance between the tumor and anal verge, CEA level, lymphovascular invasion, or tumor stage before treatment. The pathological T staging post-treatment in the interventional group was significantly reduced compared to that of the control group (p = 0.025). There were no significant differences between groups in DM rates within 1 and 2 years after surgery. In terms of DM rate within 3 years after surgery, the interventional group was significantly lower than that of the control group (9.1% vs. 29.7%, p = 0.036). Preoperative regional transarterial chemoembolization combined with concurrent chemoradiotherapy may play an important role in reducing postoperative DM in LARC.

Current monitoring and treatment for anal intraepithelial neoplasms.

Anal intraepithelial neoplasms (AIN) are precursors to anal cancer. To date, there is not a significant body of literature to support screening, monitoring, and treatment of these precursor lesions, particularly in high risk populations. This review will detail the current monitoring and indications for treatment of such lesions, with the goal of preventing progression to invasive cancer.

Management of small (T1-T2) anal margin squamous cell carcinoma: clinical outcomes following local excision alone.

Squamous cell carcinomas of the anus are normally treated with synchronous chemoradiotherapy (CRT). Small, localized anal margin tumours may be adequately treated by local excision (LE) alone. This study aims to investigate the outcomes of patients with anal margin tumours treated with LE alone, reserving the use of CRT for salvage on local recurrence (LR). Patients with small, localized (stage I/IIA) anal margin tumours treated by LE from October 1999 to September 2018 were identified. The effect of tumour size and resection margin on LR risk was analysed. Outcomes of overall survival and disease-free survival were measured. Fifty-five patients with anal margin tumours were identified. Overall 5-year LR, overall survival and disease-free survival rates were 8%, 86% and 82% respectively. Of the seven LRs, five were successfully salvaged with CRT with no further recurrence and two were not fit for CRT. Resection margins in non-fragmented tumours and tumour size did not significantly influence LR risk. Most small, localized anal margin tumours can be adequately treated by LE alone with low LR rates. Most patients who developed LR were salvaged using CRT, with no cancer-related deaths reported.

Beyond squamous cell carcinoma: MRI appearance of uncommon anal neoplasms and mimickers.

Anal cancer is an uncommon malignancy. In addition to squamous cell carcinoma, there are a variety of other less common malignancies and benign pathologies that may afflict the anal canal, with which abdominal radiologists should be familiar. Abdominal radiologists should be familiar with the imaging features that can help distinguish different rare anal tumors beyond squamous cell carcinoma and that can aid in diagnosis therefore help steer management. This review discusses these uncommon pathologies with a focus on their imaging appearance, management, and prognosis.

Inguinal nodal clinical target volume delineation based on analysis of anatomical locations of normal and metastatic lymph nodes in pelvic malignant tumors

PurposeTo optimize inguinal nodal clinical target volume (CTV) delineation based on analysis of the anatomical locations and embryonic development of normal and metastatic inguinal lymph nodes (ILNs) in patients with pelvic malignant tumors, including cervical, vaginal, vulvar, and anal tumors. Materials and methodsOne hundred and eighty-one patients with pelvic malignancies and 415 involved ILNs treated with intensity-modulated radiation therapy were selected. First, the inguinal nodal CTV was divided into three fields as follows: I, horizontal superficial inguinal field; II, vertical superficial inguinal field; and III, deep inguinal field. Initial CTV delineation of each field was based on analysis of the anatomical locations and embryonic development of normal ILNs. Subsequently, the positions of metastatic ILNs relative to the proper anatomical landmarks or vessels were determined to optimally delineate the final ILN CTV contours. Eighty percent of the data acquired (n = 145) were used as test data for optimization and analysis, the remaining 20% (n = 36) were used for delineation validation. ResultsIn total, 252 positive ILNs in 103 cervical cancer patients, 94 positive ILNs in 41 vulvar cancer patients, 8 positive ILNs in 3 vaginal cancer patients, and 61 positive ILNs in 34 anal cancer patients were enrolled. Detailed target volume contouring guidelines for the three divisions were determined on images. All positive ILNs from the remaining 20% patients were located in the CTV boundaries delineated based on analysis of 80% of the data acquired. Importantly, the final inguinal nodal CTV field determined using our method was substantially smaller than defined by existing atlases, and the femoral vessels were excluded in the delineation. ConclusionsThis study provided anatomical, embryonic, surgical, and statistical evidence to facilitate ILN CTV delineation in radiotherapy planning for patients with pelvic malignancies.