The entity "pericytoma with t(7;12)" was described as a rare, distinct perivascular myoid
neoplasm provisionally classified within the family of myopericytic
tumors that demonstrates t(7;12)(p22;q13) translocation with resultant ACTB-GLI1 fusion and biologically was felt to behave in an indolent fashion. However, a recent study showed that
tumors with this and similar translocations may have variable morphology and immunohistochemical phenotype with inconsistent myopericytic characteristics and a propensity for
metastasis, raising questions regarding the most appropriate classification of these
neoplasms. Herein, we report 3 additional patients with
tumors harboring t(7;12) and ACTB-GLI1 fusion. The
tumors arose in adults and involved the proximal tibia and adjacent soft tissues, scapula and adjacent soft tissues, and ovary. All
tumors were composed of round-to-ovoid cells with a richly vascularized stroma with many small, delicate, branching blood vessels, where the neoplastic cells were frequently arranged in a perivascular distribution. Both
tumors involving bone showed histologic features of
malignancy. By immunohistochemistry, all tested
tumors were at least focally positive for smooth muscle actin (3/3) and CD99 (patchy) (2/2), with variable staining for muscle-specific actin (2/3),
S100 protein (1/3),
epithelial membrane antigen (2/3), and pan-
keratin (1/3); all were negative for
desmin and WT1 (0/3). The 2 patients with bone
tumors developed
metastases (27 and 84 mo after diagnosis). Whether these
tumors are best classified as malignant
myopericytoma variants or an emerging translocation-associated
sarcoma of uncertain differentiation remains to be fully clarified; however, our study further documents the potential for these
tumors to behave in an aggressive fashion, sometimes over a prolonged
clinical course.