Automated Quantitative Analysis of Tissue Microarrays Reveals an Association between High Bcl-2 Expression and Improved Outcome in Melanoma

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Abstract
The addition of B-cell lymphoma 2 (Bcl-2) antisense to dacarbazine in the treatment of metastatic melanoma demonstrates improved response rates and progression-free survival when compared with dacarbazine alone. Studies on small cohorts of melanoma patients have shown variability in Bcl-2 expression (60%–96% positive). We performed quantitative analysis of Bcl-2 expression in a large patient cohort to assess the association with outcome. Tissue microarrays containing intact melanoma specimens representing 402 patients (339 with associated survival data) were analyzed with our AQUA system for automated quantitative analysis. Automated, quantitative analysis uses S100 to define pixels as melanoma (tumor mask) within the array spot and measures intensity of Bcl-2 expression using a Cy5 conjugated antibody within the mask. A continuous index score is generated, which is directly proportional to the number of molecules per unit area. Scores were divided into quartiles and correlated with clinical variables. High Bcl-2 expression was associated with better outcome in the entire cohort and among metastatic specimens only (P = 0.004 and P = 0.015, respectively). Expression was higher in primary than in metastatic specimens (P < 0.0001). There was no association between Bcl-2 expression and Breslow depth or Clark level. The diverse results within the literature may be due to use of small cohorts or variability in staining technique. These results suggest studies are needed to evaluate the association between quantitative assessment of Bcl-2 expression and response to Bcl-2 targeting therapy toward the goal of improved response rates to these drugs.