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Dogs with MCTs are generally middle aged (>5 years) and no sex predisposition is observed (Murphy et al. 2004). Breeds reported to have a high incidence of cutaneous MCTs include Boxers, Boston terriers, Weimaraners, shar‐peis, Golden retrievers, Labrador retrievers, Beagles, and Schnauzers (Murphy et al. 2004; Gieger et al. 2003; Hahn et al. 2008, 2004; Kok et al. 2019; Reynolds et al. 2019). Shar‐peis have been reported to be the breed most likely to have high‐grade MCTs, whereas the Pug and the Golden Retriever are the least likely breeds to develop high‐grade MCTs (Reynolds et al. 2019).

Figure 4.3 Surgical en bloc resection of cutaneous tumor with planned reconstructive skin fold transposition flap. (a) Preoperative skin marking of proposed en bloc tumor excision and axial skin fold transposition flap. (b) En bloc tumor excision. (c) En bloc tumor excision completed with deep margins. (d) Flank fold transposition flap raised to close tumor resection site. (e) Completed tumor resection and reconstructive procedure closure.

Source: Images courtesy of Dr. Julius Liptak.

The majority (65–80%) of cutaneous MCTs is solitary. Approximately, 50–60% of canine cutaneous MCTs occur on the trunk, with 25% occurring on the limbs and the remainder on the head and neck areas. All MCTs are locally aggressive but low‐ and intermediate‐grade MCTs have a lower metastatic potential than high‐grade MCTs. The gross appearance of cutaneous MCTs is very variable, ranging from raised hairless masses to aggressive, invasive ulcerated lesions (Figure 4.4).

Owners may report that MCT masses fluctuate in size over a short period of time. Local and paraneoplastic effects can result from release of inflammatory mediators contained within the MCT cytoplasmic granules.

MCT palpation or manipulation may cause release of histamine, leading to local redness, swelling, and pruritis. This can progress to degranulation of mast cells, producing erythema, edema, and wheal formation (Darier’s sign) (Figure 4.5).

Histamine release can cause gastrointestinal ulceration by stimulating H2 receptors on parietal cells of the stomach and increased secretion of hydrochloric acid.