Anal sac adenocarcinomas: What we have learned in the last 15 years

Epidemiology and diagnosis

Anal sac adenocarcinomas (ASCs) are uncommon tumours, thought to represent 2% of cutaneous and subcutaneous tumours. Several European studies have demonstrated a predilection for spaniel breeds^1,2, whereas most North American studies did not find any breed predilections Spaniels seem to be at a higher risk than the rest of the canine population. Historically, it was thought to affect mostly (90%) female dogs, but larger and more recent studies have proved this wrong2-5 and males were even over-represented (2/3 of cases) in 2 recent reports^6,7. No marked gender predilection is now thought to exist. In addition, ASCs appear to be non-hormone-dependant.

Anal sac carcinomas are highly metastatic tumours. Metastasis is estimated to be present at the time of diagnosis in 46% to 96% of cases, with locoregional lymph nodes (iliosacral lymphatic centre⁸ ) being the preferred sites for spreading of the disease. Invasion of the spleen, liver and uncommonly lungs can also be observed at presentation or develop later. A 5-tier staging system has been proposed for prognostic purposes: stage 1 (T2.5cm, N0, M0), Stage 3a (T1, N4.5cm, M0), stage 4 (T1, N1, M1)⁹ . [...]