ACTA1 and glomus tumor: Occasionally, glomus tumors may show unusual, atypical, or malignant features based on histologic characteristics such as nuclear atypia, infiltrative growth, vascular involvement, necrosis, or mitotic activity.2Immunohistochemical analysis typically shows positivity for α-SMA and MSA, while being negative for CD31, cytokeratins, and S100.3