A smaller 2-cm lateral margin one fascial plane deep may be adequate for complete excision of most canine cutaneous mast cell tumors. However, higher-grade tumors located on a limb may require a deeper margin. This study examined whether the currently recommended excision size of 3 cm lateral and one fascial plane deep is appropriate. Seventeen client-owned dogs with a total of 19 mast cell tumors on the neck (11%), limbs (26%), and trunk (63%) were included. Tumors were marked at 1, 2, and 3 cm from the tumor edge at 0, 90, 180, and 270 degrees. Each tumor was excised with a 3-cm lateral margin and a deep margin of at least one fascial plane. Multiple full-thickness tissue sections were evaluated along the 3-cm, 2-cm, and 1-cm margins. All tumors were assigned Patnaik grades (3 grade I and 16 grade II), and no neoplastic cells were found at the 2- or 3-cm margin in any patient. Two grade II tumors of the limb were incompletely resected at the 1-cm margin.

COMMENTARY: This study suggests that for most grade I or II canine cutaneous mast cell tumors, a 2-cm lateral margin with one fascial plane deep is adequate for complete excision. Tumors on the limb may require deeper margins of excision.

Canine cutaneous mast cell tumors: A prospective study of surgical margins. Simpson AM, Ludwig LL, Newman SJ, et al. Veterinary Cancer Society Proceedings, September 2002, p 41.