[52] A Subset of Osteosarcomas Is Positive for Nuclear Expression of P63.

Michael E Kallen, Melinda E Sanders, Adriana L Gonzalez, Justin M Cates. Vanderbilt University Medical School, Nashville, TN

Background: The p63 protein is involved in a complicated network of molecular interactions controlling cell growth and proliferation. Recently, p63 expression has been reported in the mononuclear stromal cells of giant cell tumors of bone, which are now thought likely to be osteoblast-precursor cells. Only a limited number of osteoblastic tumors have been studied for p63 expression by immunohistochemistry thus far. Therefore, we investigated whether p63 may serve as a marker for osteoblastic differentiation in a large series of osteosarcomas.
Design: 172 samples of osteosarcoma, consisting of 105 osteoblastic, 23 fibroblastic, 19 chondroblastic, 3 telangiectatic, 4 small cell, 7 parosteal, 4 low-grade intramedullary, 5 high-grade surface, and 2 periosteal subtypes from 112 patients represented on a tissue microarray were stained for the p63 tumor protein by immunohistochemistry. Associations between selected clinicopathologic parameters and nuclear or cytoplasmic p63 expression were subsequently assessed by exploratory statistical analyses. Kaplan-Meier survival curves were compared using the log-rank test.
Results: Overall, nuclear p63 was detected in only 17 of 172 (9.9%) of samples. Cytoplasmic staining was noted in an additional 41 (23.8%) of cases. There were no statistically significant associations between nuclear or cytoplasmic p63-positive cases and chemotherapy status (naïve vs. treated), specimen type (biopsy, primary resection, local recurrence or metastasis), anatomic location (appendicular vs. axial/pelvic) or histologic subtype. There were no correlations with patient age, response to neoadjuvant chemotherapy (percent coagulative tumor necrosis), or proliferative index (% Ki67-positive cells). Although none of the low-grade osteosarcomas studied were positive for nuclear p63, this association did not reach statistical significance. No differences in overall, metastasis-free or disease-free survival in p63-positive cases were detected.
Conclusions: Only a small proportion (approximately 10%) of osteosarcomas demonstrates nuclear staining for p63. This subset did not show statistically significant associations with selected clinicopathologic parameters. These findings show that p63 is not useful as a marker of osteoblastic differentiation in malignant bone tumors. However, pathologists should be aware that nuclear p63 positivity is not necessarily indicative of epithelial or myoepithelial differentiation.
Category: Bone & Soft Tissue

Tuesday, March 1, 2011 9:30 AM

Poster Session III # 1, Tuesday Morning


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