Introduction Mirvetuximab soravtansine (MIRV) is an anti-folate receptor alpha (FOLR1)-drug conjugate. Following the results of the SORAYA trail, MIRV was approved for the treatment of FOLR1-positive, platinum-resistant epithelial ovarian, fallopian tube, or primary peritoneal cancer. All 106 participants enrolled in SORAYA had high-grade serous carcinoma tumors on histology. Here, we report FOLR1 expression in gynecologic tumor histologies not represented by the SORAYA trail.

Methods Archived gynecologic tumor samples from the Stanford University Department of Pathology were retrieved. Cores of formalin-fixed paraffin-embedded tissue were arranged into tumor microarrays (TMAs). TMA slides were stained using the VENTANA FOLR1 (FOLR1–2.1) RxDx Assay. PS2 scores (percentage of tumor cells with moderate (2+) or strong (3+) staining) were assigned according to the product insert.

Results 41 cervical squamous cell carcinoma (SCC), 35 endocervical adenocarcinoma, 21 uterine serous carcinoma, 14 uterine carcinosarcoma, and 48 ovarian clear cell carcinoma (OCCC) cases were represented in the TMAs and stained with FOLR1 (see figure 1). 0% of cervical SCC, 0% of endocervical adenocarcinoma, 14% of uterine serous carcinoma, 0% of uterine carcinosarcoma, and 0% of OCCC cases met current FOLR1 positivity criteria (PS2 ≥ 75%) (see table 1).

Conclusion/Implications Variable FOLR1 expression was seen in different gynecologic tumor types. Tumor types with higher FOLR1 staining (e.g., uterine serous carcinoma) may benefit more from FOLR1-targetting therapies than low FOLR1 staining tumor types would.

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Abstract EP203/#368 Figure 1

Examples of H&E and FOLR1 staining in endocervical adenocarcinoma (A-B), uterine serous carcinoma (C-D), and ovarian clear cell carcinoma (E-F)