RARE-60. ATYPICAL RHABDOID TERATOID TUMOR: A CASE IN PREGNANCY AND ANALYSIS OF ADULT CASES TO DATE

Abstract

Atypical rhabdoid teratoid tumors (ATRT) classically develop in infancy and are rare in adults. We present the 48th case to date, the third such during pregnancy. The disease tends to follow a biphasic course i.e. if growth is not arrested following the first relapse/ progression, death is almost universal. While typically rapidly fatal, as in our case, long-term remission appears possible. Uni-variable Cox proportional-hazards models of adult cases showed significantly worse survival with: glial differentiation (HR 7.3, p<0.01), leptomeningeal dissemination (HR 4.3, p<0.01) - these were highly correlated (chi-squared <0.01) and pregnancy (HR 3.9, p=0.09). The finding that glial differentiation worsens outcomes is novel. Improved survival was seen with extent of resection (ordinal scale; p<0.01 for model) and use of craniospinal irradiation (CSI; HR 0.2, p=0.07). Systemic chemotherapy was of marginal significance (HR=0.5, p=0.13). Use of intrathecal chemotherapy was too rare to draw any conclusions. 22/46 cases originated in midline structures next to CSF, thus leading to a high rate of leptomeningeal dissemination. All 10 cases in the pituitary were in females. 3/6 cases in those aged >50 began in/beside the spinal cord. We hypothesise that the cicumventricular organs, particularly the pituitaty and pineal glands are the most common origin of these tumors. There appears to be a pool of cells dividing in the above organs, rapidly in infancy and slowly throughout much of adulthood. Review of immunohistochemistry shows ectodermal elements, with epidermal-to-mesnchymal transition; thus ATRT may be a misnomer. Loss of INI1 is neither necessary not sufficient to account for ATRT. We suggest that the development of ATRT requires an epigenetic change. Treatment options in adults differ from infants in that CSI is a viable adjunct to chemotherapy. Myelotoxicity is a concern with multimodality treatment. We suggest that facilities for peripheral blood stem-cell transplant be available.