Decreased Hsp90 expression in infiltrative lobular carcinoma: an immunohistochemical study

BACKGROUND: Elevated Hsp90 expression has been documented in breast ductal carcinomas, whereas decreased Hsp90 expression has been reported in precursor lobular lesions. This study aims to assess Hsp90 expression in infiltrative lobular carcinomas of the breast. METHODS: Tissue specimens were taken from 32 patients with infiltrative lobular carcinoma. Immunohistochemical assessment of Hsp90 was performed both in the lesion and the adjacent normal breast ducts and lobules; the latter serving as control. Concerning Hsp90 assessment: i) the percentage of positive cells and ii) the intensity were separately analyzed. Subsequently, the Allred score was adopted and calculated. The intensity was treated as an ordinal variable-score (0: negative, low: 1, moderate: 2, high: 3). Statistical analysis followed. RESULTS: All infiltrative lobular carcinoma foci mainly presented with a positive cytoplasmic immunoreaction for Hsp90. Compared to the adjacent normal ducts and lobules, infiltrative lobular carcinoma exhibited a statistically significant decrease in Hsp90 expression, both in terms of Hsp90 positive cells (%) and Allred score (74.2 ± 11.2 vs. 59.1 ± 14.2 p = 0.0001; 7.00 ± 0.95 vs. 6.22 ± 1.01, p = 0.007, Wilcoxon matched-pairs signed-ranks test). Concerning the intensity of Hsp90 immunostaining only a marginal decrease was noted (2.16 ± 0.68 vs. 1.84 ± 0.63, p = 0.087, Wilcoxon matched-pairs signed-ranks test). CONCLUSION: ILC lesions seem to exhibit decreased Hsp90 expression, a finding contrary to what might have been expected, given that high Hsp90 expression is a trait of invasive ductal carcinomas.