Clinical Oncology - Gastrointestinal: Anal Cancer

What sex is anal cancer more common in?

Females

Anal cancer makes up __ to __ of all large bowel malignancies

1%; 2%

What is the average age of diagnosis?

60 years old, and a general age distribution of 30 to 90 years old is reported

What is the main etiological factor in anal cancer?

HPV (approximately 90% of cases)

What are other etiological factors in anal cancer?

Genital warts, genital infections, anal intercourse, intercourse before 30 years old, HIV, immunosuppression, smoking

How does HPV-16 play a role in the development of cancer?

It makes proteins E6 and E7 that shuts down p53 and Rb, which are tumour suppressor proteins. When p53 and Rb are inactive, cells can become cancerous.

Describe the anatomy of the anus

3 to 4 cm long and extends from anorectal ring to anal verge

Describe the lining of the anus

Lined with hairless, stratified squamous epithelium up to dentate/pectinate line and becomes cuboidal in transition to columnar epithelium (found in rectum)

Describe the lymphatic spread of anal cancer

Lymphatic spread occurs to perirectal and anorectal nodes. If tumour extends to dentate line, nodes may include internal iliac and presacral nodes. Below the dentate line, inguinal nodes may be involved.

What is the most common symptom of anal cancer?

Rectal bleeding (bright red). Other symptoms include pain, change in bowel habits, sensation of mass.

What is a less common symptom that occurs in perianal lesions?

Pruitis

What is included in the physical examination for anal cancer?

Digital anorectal exam, palpation of inguinal lymph nodes

What is the most common pathology of anal cancer?

Squamous cell carcinoma (80%)

*Perianal Region: squamous and basal cell carcinomas, like skin cancers

Dentate Line: basaloid, cloacogenic

What is the standard treatment for anal cancer?

Combination radiation therapy and chemotherapy (5-FU and mitomycin)

What other chemotherapy drug combination is used in anal cancer?

Cisplatin and 5-FU; cisplatin is associated with less side effects and more easily tolerated by patients

What surgical procedure can be used in anal cancer?

AP resection with wide perineal dissection

When is surgery used for anal cancer?

Local recurrence after conventional chemoradiation

What conventional radiotherapy techniques were used in anal cancer?

4-field or AP/PA pelvic field with electrons to inguinal nodes, including a boost to tumour bed (electron or photon)

Describe the field borders for conventional radiotherapy for anal cancer

Superior: L5/S1

Inferior: 3 cm distal to lowest extent of tumour, includes perineal tissues which can cause skin reactions

Lateral: midlateral femoral heads to include inguinal nodes on AP field

PA: narrower than AP field as inguinal nodes do not receive much contribution from PA field, and limits does to femoral heads

AP Electron: centred over each inguinal region

What are the OARs in radiotherapy for anal cancer?

Femoral head and necks, genitilia/perineum, small bowel, bladder

What doses are used for T2 to T4 anal tumours?

4500 cGy to pelvis and inguinal nodes followed by a boost of 900 cGy to 1400 cGy to primary tumour to reduce small bowel toxicity

Total: 5400-5900 cGy