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KembaraXtra-Medicine – Anal Cancer
Anal cancer refers to malignant transformation of the mucosa within the anal canal and may be squamous, neuroendocrine, or adenocarcinoma in subtype. It is also known as anal carcinoma, cancer of the anal canal, or malignant neoplasm of anus. The ICD-10CM code listed is C21.1 (Malignant neoplasm of anal canal).
Anal cancer is uncommon, occurring at a rate of 1–2 new cases per 100,000 population, with a median age of 63 years; in HIV-infected patients, the median age is <50 years. in the united states, 2022 estimates projected 9440 new cases and 1670 deaths. worldwide, 2020 (globocan) 50,865 19,293 deaths from anal cancer. incidence has increased 2%–3% annually over last 3 decades u.s., including young black men older women. there also been an increase locally advanced (node-positive) distant-disease cases, along with mortality elderly patients.< />pan>
The rise in incidence has been noted alongside the HIV epidemic and increased rates of sexually transmitted diseases. Risk factors include HIV infection (and unlike other HIV-associated malignancies, anal cancer incidence has not decreased in the era of highly active antiretroviral therapy), human papillomavirus (HPV) infection, cigarette smoking, and sexual practice risks such as men who have sex with men (MSM), women with >10 partners, and a history of anal intercourse. Additional risks include prior sexually transmitted diseases, genital warts, prior cervical cancer, and chronic immunosuppression.
Clinical presentation is often related to tumor size and degree of infiltration. Anorectal bleeding is the most common symptom, and patients may also report anorectal pain and fullness, as well as bowel habit changes including thin-caliber stools and a sense of incomplete evacuation. However, 20%–25% of patients may be asymptomatic. Local examination may reveal skin lesions, plaques, tumors, and a background of warts. Digital rectal examination assesses sphincter function, tumor location and size, tumor extent, and possible involvement of adjacent organs (e.g., vagina, prostate, rectum). At diagnosis, most cases are localized (85%), while the remainder are advanced or metastatic; inguinal adenopathy may be present in advanced disease.
Anal cancer development is strongly linked to anogenital HPV infection, especially HPV-16 and HPV-18, which account for most cases. Most infected individuals remain asymptomatic, and only some develop dysplasia over time. HPV proteins E6 and E7 promote oncogenesis by preventing apoptosis, causing cell-cycle arrest, and contributing to genomic instability. Chronic immunosuppression (e.g., from autoimmune therapy or organ transplantation) increases genital warts and persistence of HPV infection, promoting anal intraepithelial neoplasia (AIN) and eventual cancer. In HIV infection, low CD4 counts are a risk factor for development and progression of AIN.
The differential diagnosis includes anal fissures and fistulas, anal ulcers, anorectal abscess, chancroid, genital warts, and hemorrhoids.
Workup begins with careful local assessment: local examination followed by anoscopy/proctoscopy and colonoscopy to evaluate tumor extent. Imaging includes CT scans of the chest, abdomen, and pelvis to assess nodal and distant disease; pelvic MRI for tumor detail, sphincter involvement, and mesorectal nodal evaluation; and PET scans to detect nodal involvement and to help monitor response to therapy. Biopsy of the anal lesion is required to confirm diagnosis and cancer type, and inguinal nodal biopsy may be necessary to determine metastatic involvement. Recommended diagnostic evaluation includes digital rectal examination with tumor characterization, inguinal lymph node examination with biopsy or fine-needle aspiration if suspicious, anoscopy with biopsy, and in females a gynecologic examination including cervical cancer screening. Additional evaluation includes diagnostic PET-CT of chest/abdomen/pelvis (or pelvic MRI), CBC with serum chemistries, and HIV testing with CD4 levels in patients with risk factors. Laboratory tests include CBC, a complete metabolic panel, and HIV testing.
Staging uses TNM descriptors. T categories include Tx (cannot be assessed), T0 (no evidence), Tis (carcinoma in situ--Bowen disease/HSIL/AIN II-III), T1 (≤2 cm), T2 (>2 cm to ≤5 cm), T3 (>5 cm), and T4 (any size invading adjacent organ[s]); invasion of the rectal wall, perirectal skin, subcutaneous tissue, or sphincter muscles is not classified as T4. N categories include Nx (cannot be assessed), N0 (no regional metastasis), N1 (perirectal nodes), N2 (unilateral internal iliac and/or inguinal nodes), and N3 (perirectal and inguinal nodes and/or bilateral internal iliac and/or inguinal nodes). M categories are M0 (no distant metastasis) and M1 (distant metastasis). Stage groupings are: Stage 0 (Tis N0 M0), Stage I (T1 N0 M0), Stage II (T2–T3 N0 M0), Stage IIIA (T1–T3 N1 M0 or T4 N0 M0), Stage IIIB (T4 N1 M0 or any T with N2/N3 M0), and Stage IV (any T, any N, M1).
For most anal cancers, the mainstay of therapy is nonsurgical, using radiotherapy concurrent with systemic chemotherapy. Early small tumors (T1N0)—especially on the anal margin—may be treated with local surgical resection with wide margins. In some patients, a temporary colostomy may be needed to facilitate chemoradiotherapy. Abdominoperineal resection (APR) is generally reserved as salvage for persistent disease after definitive chemoradiotherapy or for locoregional recurrence.
Historically, APR achieved surgical cures in 25%–75%, but had up to a 35% locoregional relapse rate, especially with nodal involvement. Current standard care is mitomycin plus infusional 5-fluorouracil given concurrently with pelvic radiotherapy over about 5 weeks (CRT). If response is incomplete and biopsies remain positive, options include a radiotherapy boost or salvage APR. Combined-modality CRT is superior to radiotherapy alone and improves locoregional control, progression-free survival, overall survival, and colostomy-free survival. Major toxicities include myelosuppression, infections, dermatologic toxicity, and GI toxicity. Current clinical trials are studying radiotherapy de-escalation within CRT to reduce toxicity and improve tolerability and compliance. Locoregional recurrence occurs in about 10%–30%, and 5-year survival after salvage APR is about 40%–60%.
For distant metastatic or nonsurgical advanced disease, combination chemotherapy is preferred. Triplet regimens such as docetaxel/cisplatin/5-fluorouracil (DCF) may be used in fit patients, with >80% response rates and ~25% 5-year survival. Doublets such as CF (cisplatin/5-FU) or CP (carboplatin/paclitaxel) have response rates around 60% and median overall survival ~2 years; due to favorable toxicity, CP is preferred. In chemotherapy-refractory advanced disease, options include immune checkpoint inhibitors (nivolumab, pembrolizumab, avelumab, atezolizumab), and cetuximab (anti-EGFR) may be used palliatively.
Long-term care may include colostomy care and attention to nutritional requirements. Ongoing regular follow-up and examination are recommended to detect locoregional or distant recurrence. Referral is typically made to surgical oncology, radiation oncology, and medical oncology.
No formal screening guideline exists, but high-risk individuals (e.g., chronic immunosuppression, HIV, MSM) should be considered for routine local exam with anoscopy every 4–6 months plus annual anal cytology. Prevention is expected to be influenced by HPV vaccination. Gardasil 9 protects against nine HPV subtypes. Recommendations include vaccination for all children ages 11–12, girls/women ages 13–26, boys/men ages 13–21, and high-risk men ages 22–26, with an expanded indication allowing ages 27–45 to receive catch-up vaccination. In a randomized trial of 4459 participants with biopsy-proven HSIL, active treatment (office-based ablation, ablation/excision under anesthesia, or topical fluorouracil or imiquimod) continued until HSIL resolved, with high-resolution anoscopy at least every 6 months and biopsies per protocol. Over a median follow-up of 25.8 months, progression to anal cancer was 57% lower in the treatment group than in the active-monitoring group.
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