Large studies that prove which treatment is the most appropriate one for which tumour stage are currently lacking. The ideal combination of treatments is unknown.
If the goal is to offer a temporary improvement of symptoms, then the following treatment options can be used: surgery, palliative radiotherapy, chemotherapy and/or tyrosine kinase inhibitors (kind of growth inhibitors). The efficacy of these options have not yet been definitively proven.
For the primary tumour surgery with conservation of the function of the anal sphincter is advised. Supplementary radiotherapy can result in a good local control for any remaining cancer cells.
If metastases are present chemotherapy based on carboplatin or mitoxantrone, toceranib phosphate, non-steroidal anti-inflammatory drugs, metronomic chemotherapy can be given and/or bisphosphonates for the treatment of excess calcium.
This tumour type invades the local tissues and demands a wide excision. The total excision of this tumour can be rather difficult due to the proximity of the anal sphincter. Up to half of the sphincter can be excised without causing nerve damage. When more than half needs to be removed or when the tumour is situated on the left as well as on the right side of the anus, surgical excision can lead to nerve damage. The consequences include the loss of sphincter control and thus loss of control of defecation.
The swollen lymph nodes can also be removed, certainly when they cause obstruction of the pelvis and/or cause an excess of calcium blood levels. When the tumour can only be removed with little margin, the risk of recurrence is high. This is also the case when the distinction between healthy and tumoural tissue is difficult. Complications occur in about 10% of surgically treated cases. The most common complications include bleeding during the operation, infection, incontinence (fecal or urinary), squeezing to defecate and the formation of fistulas.
This treatment is advised when the tumour cannot be removed in its entirety. Up to 38% of dogs had a reduction in tumour size after radiotherapy and in 62% of dogs with clinical symptoms there was an improvement of disappearance of symptoms after radiotherapy.
So far, little is documented about the effect of chemotherapy as monotherapy or as a supplementary treatment for anal sac adenocarcinomas.
No impressive results were reported for chemotherapy (mitoxantrone, carboplatin, cisplatin, actinomycin D, melphalan) in monotherapy and their role in combination with other treatments is unknown.
Toceranib phosphate (tyrosine kinase inhibitor) is associated with a mild response (decrease in tumour volume).
Non-steroidal anti-inflammatory drugs have no proven effect so far, but their general affect against the formation of new blood vessels and tumour development could decrease the tumour growth.