PMEL and neoplasm with perivascular epithelioid cell differentiation: However, it is important to remember that PEComas were defined as tumors characterized by the presence of perivascular epithelioid cells (PECs), unique cells able to “modulate its morphology and immunophenotype... [which] can show muscular features with a spindle shape and a stronger positivity for actin than for HMB45 or it can have an epithelioid feature with a strong positivity for HMB45 and a mild, if any, reaction for actin” [62].