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Updated: Jan 11, 2026
Heterogeneity Mapping of Protein Expression in Tumors using Quantitative Immunofluorescence
Published on: October 25, 2011
Heterogeneity and Scoring Reproducibility of Folate Receptor 1 Immunohistochemistry in High-grade Serous Carcinoma
Brooke Liang1, Troy B Tenney2, Lucy Han3
1Department of Pathology, Stanford University School of Medicine, Stanford.
Abstract:
Mirvetuximab soravtansine (MIRV) is an antibody-drug conjugate approved for the treatment of adult patients with folate receptor 1 (FRα; FOLR1) positive, platinum-resistant epithelial ovarian, fallopian tube, or primary peritoneal cancer, who have received one to three prior systemic treatment regimens. Per the FDA approval, FOLR1 positivity is defined as ≥75% of viable tumor cells showing moderate (2+) or strong (3+) membranous immunostaining ("PS2+"). Given this disease's high recurrence rate and relatively limited therapeutic options, there is utility in exploring consistency in FOLR1 reporting. Tubo-ovarian high-grade serous carcinoma (HGSC) samples from our institution's archives were included in tissue microarrays (n=806), whole tissue sections (n=51), or cell blocks (n=30) and evaluated using the Ventana FOLR1 (FOLR1-2.1) RxDx Assay. FOLR1 staining was heterogeneous across different anatomic sites (average FOLR1 PS2+ was 50.2 from adnexal sites compared with 47.4 from omental sites, P =0.015). Similarly, heterogeneity was noted in pre- versus post- neoadjuvant chemotherapy specimens (on average, FOLR1 PS2+ score increased by 17.7 from pre- to post- therapy, P =0.0089). Lastly, specimen type may also influence FOLR1 staining (average abdominal fluid FOLR1 PS2+ score was 25.5 and average surgical FOLR1 PS2+ score was 56.9, P =0.000034). Agreement among 9 readers was initially substantial, with a Fleiss kappa of 0.661 (95% CI: 0.636-0.685). For the subset of cases with the worst agreement initially, a training session with reference cases improved interobserver agreement. Our study highlights several factors contributing to heterogeneity in FOLR1 reporting. Future studies are needed to better understand the impact of FOLR1 heterogeneity on patient response to therapy.
Insights
Folate receptor 1 (FRα) reporting in ovarian cancer shows significant heterogeneity across different tumor sites, specimen types, and after chemotherapy. This variability impacts diagnostic consistency for targeted therapies like mirvetuximab soravtansine.
Area of Science:
- Oncology
- Pathology
- Translational Medicine
Background:
- Mirvetuximab soravtansine (MIRV) is approved for FRα-positive, platinum-resistant ovarian cancer.
- FOLR1 positivity requires ≥75% tumor cells with moderate/strong membranous staining (PS2+).
- Ovarian cancer has a high recurrence rate and limited treatment options, necessitating consistent biomarker reporting.
Purpose of the Study:
- To evaluate the consistency of Folate Receptor 1 (FOLR1) reporting in tubo-ovarian high-grade serous carcinoma (HGSC).
- To identify factors contributing to heterogeneity in FOLR1 immunostaining.
- To assess the impact of specimen type and treatment on FOLR1 expression.
Main Methods:
- Analysis of 806 tissue microarrays, 51 whole tissue sections, and 30 cell blocks from tubo-ovarian HGSC using the Ventana FOLR1 (FOLR1-2.1) RxDx Assay.
- Evaluation of FOLR1 staining heterogeneity across different anatomic sites, pre- vs. post-neoadjuvant chemotherapy, and specimen types (surgical vs. abdominal fluid).
- Assessment of interobserver agreement among 9 readers, with subsequent training to improve concordance.
Main Results:
- Significant FOLR1 staining heterogeneity was observed across anatomic sites (adnexal vs. omental) and specimen types (surgical vs. abdominal fluid).
- FOLR1 expression increased post-neoadjuvant chemotherapy, indicating treatment-induced changes.
- Initial interobserver agreement was substantial (Fleiss kappa = 0.661), but improved after a training session.
Conclusions:
- Multiple factors, including anatomic site, specimen type, and prior chemotherapy, contribute to FOLR1 reporting heterogeneity in ovarian cancer.
- Understanding and mitigating this heterogeneity is crucial for accurate patient selection for FRα-targeted therapies.
- Further research is needed to determine the clinical impact of FOLR1 heterogeneity on treatment response.
