Folate Receptor Alpha Immunohistochemistry in Cytology Specimens of Metastatic Breast Carcinoma

Abstract

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.

Utility of folate receptor alpha immunohistochemistry in cytology specimens of metastatic breast carcinoma, metastatic serous carcinoma of Müllerian origin, and primary lung adenocarcinoma

“…The variable cellular adequacy of the CB can always be a limiting factor. To eliminate low cellularity of the CB as a limiting factor, we previously reported concordance between the results of FRA IHC using mAb BN.3 clone (Leica Biosystems Leica Biosystems, Bannockburn, IL) in CB and surgical specimens (including both needle core biopsies and resection specimens) of TNBC cases . Tumor heterogeneity can also be a limiting factor in assessing FRA IHC in CB.…”

“…Of note, all the prior studies for FRA IHC have been conducted on surgically excised tissue specimens obtained exclusively from primary breast cancers except O'Shannessy et al who used both primary and metastatic breast cancer specimens . We previously reported the FRA expression in cytology CB of metastatic TNBC cases using a different commercially available clone of FRA, monoclonal antibody BN3.2; 1:100 dilution; Leica Biosystems, Bannockburn, IL, and found FRA positivity in only 4% of metastatic TNBC cases …”

“…Currently, there is not an established scoring system for FRA IHC and no guidelines are available for clinical testing and reporting. Almost all the previous studies have been performed in the surgical specimens and only few studies have used FRA IHC in CB material . At this point, it will be extremely difficult to predict the limitations of using the CB to analyze FRA by IHC.…”

“…FRA IHC staining intensity was scored as 0 (negative), 1+ (weak), 2+ (moderate), or 3+ (strong), and by staining area (0–100%). Cases were scored as qualitatively positive (reactive) if at least 1+ staining was observed in >10% of tumor cells as previously reported …”

Nanomedicine applications in the treatment of breast cancer: current state of the art

“…66 There is concern that folate receptor is also expressed in normal tissues, but it is argued that nanodelivery to these tissues should be limited as the receptor is restricted to the lungs, kidneys, placenta and choroid plexus, and in these tissues, the receptor is limited to the apical surface which is poorly accessible. 69 Other than folate receptor, C-X-C chemokine receptor type 4 is a potentially useful TNBC cell target, as it is often highly expressed in TNBC cells.…”