Anal cancer is a relatively uncommon malignancy. It accounts for less than 2% of large bowel malignancies and 1-6% of anorectal tumours (~1.5% of all gastro-intestinal tract malignancies in the Unites States 14).
There may be a slight male predilection where its incidence has been reported to be approximately 0.5 per 100 000 in men and 1.0 per 100 000 in women 1. Its incidence is thought to be rising over the years 5.
Approximately 45% of patients may present with bleeding per rectum. Around 30% of patients may have pain and/or a sensation of a mass.
Anal carcinoma typically originates between the anorectal junction above and the anal verge below. The vast majority of anal canal cancers are squamous cell cancers. See WHO classification of anal canal tumours.
Both male and female 15:
- HPV / HIV infection
- number of lifetime sexual partners, and receptive anal intercourse
In females: previous in situ or invasive cervical, vulval or vaginal cancer 15.
- tumour above dentate line: to pararectal and paravertebral nodes 13
- tumour below dentate line: to inguinal and femoral nodes 13
Imaging performed prior to treatment provides assessment of the local disease extent and nodal involvement. Accurate delineation of the disease in relation to the rest of the perineal anatomy is of paramount importance in initial imaging assessment. The size of the tumour is also considered a very important prognostic factor (see staging) 13.
MRI is the modality of choice in the assessment of locoregional disease. This generally requires a dedicated protocol: see MRI protocol for assessment of anal cancer.
Reported usual signal characteristics include 2
- T1: primary and recurrent tumours are usually of low to intermediate signal intensity relative to skeletal muscle
- T2: primary and recurrent tumours are usually of high signal intensity relative to skeletal muscle
Nodal metastases are of similar signal intensity to the primary tumour.
Recent research suggests PET/CT being useful that it alters the initial staging sufficiently frequently that it should be used routinely in anal cancer, where it is available 4. At the time of initial writing (2012), the role of PET/CT in the follow-up of anal cancer is not as clear 4.
Sometimes can be used in the locoregional staging 6. Some authors suggest that endoanal ultrasound can accurately determine the depth of penetration of the carcinoma into the sphincter complex and can be used to gauge accurately the response of these tumors to chemoradiation therapy 8.
Anal cancer is usually staged using the TNM system. See: staging of anal cancer
Treatment and prognosis
Treatment is often with a using a combination of chemotherapy and radiotherapy (often given concurrently) and is considered to be usually curative. Approximately 50-60% are thought to present with T1 to T2 lesions carrying a 5 year survival of 80-90% 3. Some authors suggest a benefit of a salvage abdominoperineal resection (APR) for those patient with failed chemoradiation 10,12.
- 1. Koh DM, Dzik-jurasz A, O'neill B et-al. Pelvic phased-array MR imaging of anal carcinoma before and after chemoradiation. Br J Radiol. 2008;81 (962): 91-8. doi:10.1259/bjr/96187638 - Pubmed citation
- 2. Roach SC, Hulse PA, Moulding FJ et-al. Magnetic resonance imaging of anal cancer. Clin Radiol. 2005;60 (10): 1111-9. doi:10.1016/j.crad.2005.05.008 - Pubmed citation
- 3. Schäfer A, Langer M. MRI of Rectal Cancer. Springer Verlag. (2009) ISBN:3540728325. Read it at Google Books - Find it at Amazon
- 4. Wells IT, Fox BM. PET/CT in anal cancer - is it worth doing? 2011;doi:10.1016/j.crad.2011.10.030 - Pubmed citation
- 5. Wan M, Meacock L, Summers J et-al. 11. MR imaging of anal cancer: a pictorial review. Cancer Imaging. 2011;11 Spec No A : S181. doi:10.1102/1470-7330.2011.9074 - Pubmed citation
- 6. Parikh J, Shaw A, Grant LA et-al. Anal carcinomas: the role of endoanal ultrasound and magnetic resonance imaging in staging, response evaluation and follow-up. Eur Radiol. 2011;21 (4): 776-85. doi:10.1007/s00330-010-1980-7 - Pubmed citation
- 7. Jacopo M. Endoanal ultrasound for anal cancer staging. Int J Colorectal Dis. 2011;26 (3): 385-6. doi:10.1007/s00384-010-0998-2 - Pubmed citation
- 8. Tarantino D, Bernstein MA. Endoanal ultrasound in the staging and management of squamous-cell carcinoma of the anal canal: potential implications of a new ultrasound staging system. Dis. Colon Rectum. 2002;45 (1): 16-22. - Pubmed citation
- 9. Herzog U, Boss M, Spichtin HP. Endoanal ultrasonography in the follow-up of anal carcinoma. Surg Endosc. 1994;8 (10): 1186-9. - Pubmed citation
- 10 .Billingham RP. Reoperative Pelvic Surgery. Springer Verlag. (2009) ISBN:0387899987. Read it at Google Books - Find it at Amazon
- 11. Beck DE, Roberts PL, Saclarides TJ et-al. The Ascrs Textbook of Colon and Rectal Surgery. Springer Verlag. (2011) ISBN:1441915818. Read it at Google Books - Find it at Amazon
- 12. Ryan DP, Mayer RJ. Anal carcinoma: histology, staging, epidemiology, treatment. Curr Opin Oncol. 2000;12 (4): 345-52. Curr Opin Oncol (link) - Pubmed citation
- 13. Ryan DP, Compton CC, Mayer RJ. Carcinoma of the anal canal. N. Engl. J. Med. 2000;342 (11): 792-800. doi:10.1056/NEJM200003163421107 - Pubmed citation
- 14. Bendell JC, Ryan DP. Current perspectives on anal cancer. Oncology (Williston Park, N.Y.). 2003;17 (4): 492-7, 502-3. - Pubmed citation
- 15. Serup-Hansen E, Linnemann D, Skovrider-Ruminski W et-al. Human papillomavirus genotyping and p16 expression as prognostic factors for patients with American Joint Committee on Cancer stages I to III carcinoma of the anal canal. J. Clin. Oncol. 2014;32 (17): 1812-7. doi:10.1200/JCO.2013.52.3464 - Pubmed citation