Anal sac carcinoma
radiation therapy for dogs
in Florida.

Local and regional control
require more than surgery alone.

Anal sac adenocarcinoma is staged by tumor size and lymph node involvement — and over half of dogs have sublumbar lymph node metastasis at diagnosis. Surgery can remove the primary tumor and accessible nodes, but radiation plays a critical role in treating residual microscopic disease and managing lymph node recurrence.

The initial presentation is often incidental — a mass found on rectal palpation during a routine exam — or driven by signs of local disease: difficulty defecating, perianal swelling, or scooting. The association with hypercalcemia means that blood work revealing elevated calcium in an older dog should always prompt evaluation of the anal sacs, even if no mass is clinically obvious.

Sublumbar lymph nodes — the critical target

The sublumbar (internal iliac) lymph nodes are the primary regional draining nodes for ASAC and are frequently involved at diagnosis. When enlarged, they can compress the colon and urethra — causing constipation, difficulty urinating, and significant pain. Radiation to these nodes can decompress these structures and restore function, even when surgical removal is not feasible or complete.

The role of radiation in ASAC

Adjuvant radiation after surgery targets the primary surgical bed and any residual lymph node disease, reducing local recurrence significantly. For cases where lymph nodes cannot be fully resected, palliative radiation to the sublumbar region relieves compression, restores defecation and urination, and improves quality of life meaningfully. Radiation is also used as the primary local treatment in inoperable cases.