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Mast cell tumors that are strictly subcutaneous (tumors that do not involve the cutaneous layer at all) are their own clinical entity. Overall, subcutaneous MCTs have a relatively good prognosis with prolonged survival (>1500 days) (Thompson 2011; Gill et al. 2020). Survival probabilities are 93–95%, 92–95%, and 86% at one, two, and five years, respectively (Thompson 2011; Gill et al. 2020). The grading schemes from Patnaik and Kiupel were developed for cutaneous mast cell tumors and may not be appropriate for prognostication. For example, the lowest grade a subcutaneous MCT can be using the Patnaik scale is II, because as soon as the tumor goes into the subcutaneous area, the tumor is defined as at least a grade II. When these grading schemes were applied to subcutaneous tumors, 98% were grade II on the Patnaik scale and 96% were low grade on the Kiupel scale and this was not prognostic (Gill et al. 2020). Negative prognostic factors for survival for subcutaneous MCTs are mitotic index, infiltrative growth (i.e. lack of tumor demarcation), and presence of multinucleation (Thompson 2011). Local recurrence is 7–8%. Although incomplete margins are a negative prognostic factor, local recurrence with incomplete margins are low (12–21%) (Thompson 2011; Gill et al. 2020). Mitotic index is a prognostic factor for local recurrence (Thompson 2011).