Background: Folate receptor alpha (FRA) is involved in folate accumulation and utilization, and is expressed in varying proportions in breast, ovary and parotid epithelial cells, among others. FRA overexpression by immunohistochemistry (IHC) has been shown in estrogen/progesterone receptor (ER/PR)-negative carcinoma (40-74%) and in triple-negative breast carcinoma (TNBC; 50-86%) in histological specimens of primary breast cancers. We assessed the feasibility of IHC in detecting FRA expression and its patterns and clinical significance in metastatic TNBC in fine-needle aspiration (FNA) cell blocks (CBs). Materials and Methods: Metastatic breast ductal carcinoma cases were retrospectively immunostained with FRA IHC on FNA CBs. FRA staining was scored qualitatively (+/-), by intensity (0-3) and by staining area (0-100%). Of these metastatic cases, a subset of primary breast carcinoma cases was also immunostained with FRA. The results were correlated with ER, PR and human epidermal growth factor receptor 2 (Her2/Neu) performed by routine IHC. Results: A total of 40 FNA CBs with metastatic disease were studied, including hormone (ER/PR) positive (n = 5), triple positive (n = 5), Her2/Neu-only positive (n = 5) and TNBC (n = 25). FRA IHC showed immunoreactivity with moderate positivity in only 1 (4%) TNBC. All the remaining 39 cases were negative for FRA expression. Five cases of primary TNBC were stained with FRA IHC and were negative for FRA expression. Conclusions: Our data suggest that FRA expression by IHC was rarely associated with ER/PR-negative tumors relative to ER/PR-positive tumors and, more importantly, with TNBC in FNA CBs. This finding may have a clinical significance and prognostic implications in metastatic breast carcinoma. Furthermore, 5 primary TNBC cases did not overexpress FRA by IHC. Hence, antifolate receptor therapies do not appear to be clinically relevant in TNBC based on immunostaining of FNA CBs of metastatic breast cancers.

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