Others

Mucinous (colloid) adenocarcinoma: in anal fistula which may be associated with Crohn's disease or hindgut duplication.

Anal gland adenocarcinoma: rare. In contrast to anorectal adenocarci-noma lacks O-acetylsialomucin (PAS negative post PB-KOH saponification). Late diagnosis, poor prognosis.

Extra-mammary Paget's disease: in 20% an underlying adnexal or rectal adenocarcinoma is found. The majority remain confined to the surface epithelium.

Neuroendocrine carcinoma: carcinoid/small cell/large cell; carcinoid <2 cm is treated by local excision, if >2 cm consider more radical surgery.

Figure 7.3. Anal canal carcimoma. |W Spindle cell carcinoma: rare.

Squamous cell carcinoma with microcysts: worse prognosis.

Malignant melanoma: primary mucosal origin with adjacent junctional atypia that can be destroyed by surface ulceration. 1.5% of anal malignancy—aggressive with early spread and death in months (liver, lung metastases). Spindle cell or epithelioid.

Metastatic carcinoma: direct spread—adenocarcinoma of rectal type arising from the colorectal mucosa of the upper anal zone cannot be distinguished from usual low rectal carcinoma and is grouped with it. Prostatic carcinoma (PSA/PSAP positive) and cervical carcinoma.

3. DIFFERENTIATION

Well/moderate/poor/undifferentiated or Grade 1/2/3/4.

For squamous cancers differentiation features are keratinization and intercellular bridges, and for adenocarcinomas the percentage tumour gland formation (well/G1 >95%; moderate/G2 50-95%; poor/G3 <50%). Undifferentiated carcinomas (no gland formation) are classified as grade 4.

Sarcoma: low-grade/high-grade based on necrosis, atypia and mitotic counts.

4. EXTENT OF LOCAL TUMOUR SPREAD

Border: pushing/infiltrative. Lymphocytic reaction: prominent/sparse.

Depth of spread: submucosa; muscularis of rectum or anal sphincters; extrarectal and extra-anal tissue including ischiorectal fossae and pelvic structures. Clinical assessment is by MRI and endoanal ultrasound for local spread, and CT scan for distant disease.

Figure 7.4. Anal canal carcinoma.

Tumour of any size invades adjacent organ(s) eg vagina, urethra, bladder. Direct invasion of the rectal wall, perianal skin, subcutaneous tissue or the sphincteric muscle(s) alone is not classified as pT4.

Figure 7.4. Anal canal carcinoma.

At diagnosis the majority have spread through sphincteric muscle into adjacent soft tissue.

The TMN classification applies only to carcinomas.

pTis carcinoma in situ pT1 tumour < 2 cm in greatest dimension pT2 2 cm < tumour < 5 cm in greatest dimension pT3 tumour > 5 cm in greatest dimension pT4 tumour of any size invading adjacent organ(s), e.g. vagina, urethra, bladder.

5. LYMPHOVASCULAR INVASION

Present/absent. Intra-/extratumoral. Perineural spread.

Distant metastases at the time of diagnosis are present in 5-10% of cases. Haematogenous spread is to liver, lung and skin.

6. LYMPH NODES

Site/number/size/number involved/limit node/extracapsular spread. Regional nodes: perirectal, internal iliac, inguinal. Anal margin tumours go initially to inguinal nodes ^ iliac nodes. Anal canal tumours go initially to haemorrhoidal nodes ^ perirectal and inguinal nodes. A regional lymphadenectomy will ordinarily include a minimum of 12 lymph nodes.

pN0 no regional lymph node metastasis pN1 metastasis in perirectal lymph node(s)

pN2 metastasis in unilateral internal iliac and/or inguinal lymph node(s)

pN3 metastasis in perirectal and inguinal lymph nodes and/or bilateral internal iliac and/or inguinal lymph nodes.

Lymph node involvement is present in 10-50% of cases at presentation.

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