[63] Neoadjuvant Radiation: Effect on Immunohistochemical Marker Expression in Soft Tissue Tumors.

Bojana Mitrovic, Richard Kirsch, Peter W-M Chung, Peter C Ferguson, Jay S Wunder, Brendan C Dickson. Mount Sinai Hospital, Toronto, ON, Canada; UHN Princess Margaret Hospital, Toronto, ON, Canada

Background: It is generally assumed that immunohistochemistry is unreliable in the setting of neoadjuvant radiation; however, there is limited published data to support this view. The aim of this preliminary study is to assess the reliability of immunohistochemistry in the context of neoadjuvant radiation by comparing the staining patterns of commonly used markers in soft tissue tumors before and after radiation.
Design: We prospectively identified soft tissue tumors resected after neoadjuvant radiation at our institution. The expression of a broad array of markers, with emphasis on common stains such as AE1/AE3, S100, smooth muscle actin, desmin and CD34, was evaluated and compared between pre- and post-treatment specimens.
Results: A total of 24 neoadjuvant specimens were examined: 1 clear cell sarcoma, 1 epithelioid sarcoma, 1 extraskeletal myxoid chondrosarcoma, 1 fibrosarcoma, 1 leiomyosarcoma, 5 liposarcomas, 2 rhabdomyosarcomas (pleomorphic), 3 sarcomas of unknown histogenesis, 1 solitary fibrous tumor, 4 synovial sarcomas and 4 undifferentiated pleomorphic sarcomas. Immunohistochemistry was available on 17 corresponding pre-treatment biopsies. Only minor discrepancies were identified between pre- and post- treatment specimens. Loss of expression was seen in two cases: a clear cell sarcoma with weak expression of synaptophysin that was lost post-therapy, and a rhabdomyosarcoma with focal Myf-4 expression that was lost post-therapy. Post-therapy gain of expression was seen in three cases: a solitary fibrous tumor gained focal AE1/AE3 expression; a synovial sarcoma gained epithelial membrane antigen expression; and another synovial sarcoma gained focal S100 expression.
Conclusions: Overall, there was generally concordance of immunophenotype comparing pre- and post-radiation specimens. Differences were focal and in some cases likely attributable to sampling issues. The loss of Myf-4 in a rhabdomyosarcoma was unexpected and it is unclear whether this reflects altered transcriptional activity due to radiation. Focal keratin expression occasionally occurs in solitary fibrous tumors and it is possible this was exacerbated by radiation. Neoadjuvant radiotherapy appears to minimally affect the immunophenotype of soft tissue tumors, suggesting that immunohistochemistry may retain diagnostic value in the post-neoadjuvant setting. Confirmation of these preliminary findings in a larger cohort is required.
Category: Bone & Soft Tissue

Tuesday, March 1, 2011 9:30 AM

Poster Session III # 25, Tuesday Morning


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