[849] ERG Immunohistochemical Expression in Dominant Prostate Cancers and Paired Lymph Node Metastases

Samson W Fine, Hikmat A Al-Ahmadie, Ying-Bei Chen, Maria Dudas, Satish K Tickoo, Victor E Reuter, Anuradha Gopalan. Memorial Sloan-Kettering Cancer Center, New York, NY

Background: TMPRSS2-ERG gene fusions occur in about 50% of prostate cancers with resultant overexpression of a protooncogene, ERG. ERG overexpression by immunohistochemistry is a good surrogate for ERG gene rearrangement. Prior studies have revealed that ERG expression can vary both within and between tumor nodules in a given prostate. In cases with lymph node metastasis, positive lymph nodes contralateral to the dominant primary tumor may be seen in 30-40% of cases, suggesting significant “crossover” of lymphatic channels. The relationship of ERG status in dominant (largest) primary prostate cancers and matched lymph node metastases has not been well studied.
Design: 15 cases of primary prostate cancer and paired lymph node metastases were selected for study. Group 1 (n=9 cases) had bilateral positive lymph nodes with unilateral dominant primary tumors, while Group 2 (n=6 cases) had unilateral positive lymph nodes with unilateral dominant primary tumors contralateral to the side of lymph node metastasis. Multiple areas from the primary cancer, including high and low grade foci, were arrayed in triplicate in a single TMA. ERG immunohistochemistry was performed on sections from the TMA and whole sections from positive lymph nodes.
Results: ERG status of primary tumors:
12 of 15 cases had both high and low grade foci available for sampling and in 11 of these cases ERG status was concordant for all grades. Group 1: 9/9 cases had matching ERG status for all grades. Group 2: 2/6 cases had matching ERG status for all grades; 1/6 had discordant ERG status in different grades (low grade - negative, high grade - positive); 3/6 had only high grade areas which were concordant for ERG status.
Comparison of ERG status between positive lymph nodes and primary tumors:
Group 1: 9/9 cases – ERG status matched that of the dominant tumor; Group 2: 6/6 cases – ERG status matched that of dominant tumor. In the single case with discordant ERG status between low and high grade areas, the ERG status in the positive lymph node matched that of the high grade component.
Conclusions: ERG status of positive lymph nodes is concordant with ERG status of the dominant primary tumor. This is true even when the dominant tumor is contralateral to the metastasis, supporting the existence of lymphatic crossover. Within a given tumor, ERG status of low and high grade foci is usually concordant. Further studies are ongoing to investigate ERG status in cases with positive lymph nodes and more than one dominant/high grade primary tumor nodule to better assess the clonality of these metastatic lesions.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 1:00 PM

Poster Session II # 177, Monday Afternoon

 

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