23. Anal Cancer - The GEC-ESTRO Handbook of Brachytherapy

Anal Cancer

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THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 01/03/2023

10% to 15% of patients will have cancer that has spread beyond the pelvis at diagnosis. Most relapses after curative therapy (which concern 10% to 30% of patients) are in the pelvis, perineum, or inguinal regions. As the number of metastatically involved regional nodes increases, so does the risk of distant metastasis. The most common site of distant metastasis are the liver and lungs. Although chemotherapy is a component of standard therapy for anal cancer, its addition has not decreased the number of patients who develop distant metastases [6]. The size and extent of the primary tumour, and inguinal or pelvic nodal involvement have significant prognostic value, both for survival and local control [7]. Risk factors for anal cancers include: - Sexual behavior: number of sexual partners, age at first sexual intercourse, practice of receptive anal intercourse - Sexually transmitted viruses: HPV infection andHIV infection, especially in men who have sex with men. HPV DNA has been identified in most anal tumours - Chronic immunosuppression, especially in renal transplant patients - Cigarette smoking Benign anal conditions, such as anal fissure, fistula, perianal abscess, and haemorrhoids, are more often a symptom or misdiagnosis rather than a cause of anal cancer. History and physical examination Evaluation of the patient with known or suspected anal cancer should begin with a thorough history and physical examination (figure 2). The patient should be questioned about anal sphincter function and any history of risk factors for HIV infection (sexual or drug abuse). In addition to a complete general physical examination, a detailed examination should be conducted of the abdomen, inguinal region, anus, and rectum. To perform anal brachytherapy, it is essential to have a precise clinical description of the tumour before the treatment, and preferably this evaluation will be performed by the brachytherapist who will perform the procedure [8]. The extent of circumferential involvement of the anal canal should be noted, and the size, extent, and location of the primary tumour should be documented, ideally summarized in a diagram [9] (figure 3 shows an example of such diagram). More precisely, the location of the tumour must be specified in all planes: circumferential extension expressed in the hourly quadrant, specifying the patient's position (supine or genupectoral position), distance of the lower pole from the anal margin and possible skin extension, height, and estimation of the depth (MRI and endorectal ultrasound can complement the physical examination here). The size, location, and mobility of palpable inguinal lymph nodes should also be noted. Perirectal lymph nodes may be involved, but these are rarely palpable by digital rectal examination. 5. WORK UP

Figure 1: Anatomy of the anal region

The anal canal is surrounded by the internal and external sphincters, which play a major role in faecal continence. Indeed, except during defecation, those sphincters collapse the anal canal to prevent the passage of faecal material. The internal anal sphincter surrounds the upper two-thirds of the canal, whilst the external anal sphincter surrounds the lower two-thirds of the canal, and so overlaps with the internal sphincter. At the junction of the rectumand the anal canal, there is amuscular ring, known as the anorectal ring, and is palpable on digital rectal examination. The pectinate line (or dentate line) divides the anal canal into upper and lower parts, which differ in both structure and neurovascular supply. Squamous cell cancer, also known as epidermoid carcinoma, is the most frequent histological type of anal cancers, accounting for 80-85% of cases [4]. According to the world health organization (WHO) classification, the other histological types include adenocarcinoma, mucinous adenocarcinoma, small cell carcinoma, and undifferentiated carcinoma. Adenocarcinomas require the incorporation of surgery into the initial management of the cancer [5]. Unlike most gastrointestinal tract malignant diseases, anal cancer is predominantly a locoregional disease, and distant metastasis is relatively rare. At diagnosis, about half of all anal cancers have been found to invade the anal sphincter or surrounding soft tissue. Although rectoprostatic fascia (Denonvilliers fascia) is usually an effective barrier to prostatic invasion in men, direct extension to the rectovaginal septum is a common occurrence in women. Only 4. PATHOLOGY