Uterine neoplasms composed of rhabdoid cells do not exhibit loss of INI1 immunoreactivity and are not related to childhood malignant rhabdoid tumor

Malignant rhabdoid tumors are rare childhood neoplasms which occur most commonly in the kidneys, soft tissue, and central nervous system. They are characterized by cells with eccentric vesicular nuclei, prominent nucleoli, and abundant eosinophilic-cytoplasm. Recently, it has been demonstrated that malignant rhabdoid tumors in childhood are characterized by biallelic deletion or mutation involving the SMARCB1/INI1 gene on chromosome 22. These molecular events result in loss of immunohistochemical expression of INI1. Neoplasms with a similar morphology occur in adults, either in pure form or associated with a parent tumor. It is controversial whether such neoplasms in adults are related to childhood malignant rhabdoid tumor or whether a rhabdoid morphology represents a nonspecific phenotype which can occur in a variety of neoplasms. In this study, we stained a series of adult uterine neoplasms with a prominent component of rhabdoid cells with the Baf 47 antibody which detects INI1; we aimed to ascertain whether these are related to childhood malignant rhabdoid tumor. Neoplasms included were an undifferentiated sarcoma consisting entirely of rhabdoid cells, 2 carcinosarcomas with a mesenchymal component composed entirely of rhabdoid cells, and 3 uterine tumors resembling ovarian sex cord tumor with rhabdoid cells. In all cases, there was positive nuclear staining of the rhabdoid cells with Baf 47, suggesting an absence of gene deletion or mutation and that these neoplasms are not related to childhood malignant rhabdoid tumor. In adults, we suggest that a diagnosis of malignant rhabdoid tumor should not be made without genetic confirmation or loss of immunohistochemical expression of Baf 47. In the absence of these, an attempt should be made to classify such tumors on the basis of any associated parent neoplasm and/or immunohistochemical or ultrastructural evidence of specific differentiation. We reviewed uterine neoplasms with a rhabdoid phenotype.