Benign tumours (adenomas) can arise from perianal glands and their development and growth seem to be linked with sex hormones. The growth of these tumours is stimulated by male hormones and suppressed by female. Of note, the prevalence of these tumours regularly coincides with certain testicular tumours (Leydig cell tumour). Perianal adenomas only appear in bitches when their uterus and ovaries have been removed, although they are also known to appear in exceptional cases of excessive adrenal production of testosterone. Perianal adenomas grow slowly. They can become very large locally, but do not metastasize.
These tumours appear in both intact as well as neutered male and female dogs. Malignant tumours have a tendency to grow faster than benign ones, be less mobile and firmer. Perianal adenocarcinomas metastasize infrequently (in about 15% of cases). The most frequent places metastases occur are the local lymph nodes, seldom the lungs, liver, kidneys and bone.
The benign form (adenoma) occurs relatively frequently (more than 50% of tumours around the anus), at an average age of 10 years, whilst the malignant form (adenocarcinoma) appears less frequently (between 3-21% of tumours around the anus) at an average age of 11 years.
The benign form occurs more in the beagle, Bulldog, Cocker Spaniel and Samoyeed, whereas the malignant form mainly affects males of large breeds.
- Benign form: slowly growing (during months or years) tissue mass(es) which aren’t painful and usually aren’t associated with anomalies. They can also occur on the foreskin, ball sac or tail. These tissue masses can ulcerate and infect, but are rarely attached to the underlying structures. Usually, they are well delineated (average of 0.5 to 3 cm in diameter) and raised.
- Malignant form: this form resembles the benign one, but grows faster, is firmer, ulcerates, attaches to underlying tissues, relapses when the surgical margins were very narrow and is generally larger than the benign form. Large tissue masses are likely to cause obstruction and difficulties defecating, pain or irritation around the anus. Although rarely the case, metastases in the abdominal lymph nodes can significantly enlarge the affected lymph nodes. In turn, this causes pressure on the intestines and complicates bowel movements.