Ramoth, Johanna

Abstract Purpose Delta-like protein 3 (DLL3) is being developed as a predictive biomarker for DLL3-targeting antibody-drug conjugate and other therapies. Given the neuroendocrine features of Merkel cell carcinoma (MCC), we sought to evaluate DLL3 expression and its role in MCC. Experimental Design Formalin-fixed and paraffin-embedded MCC cases were consecutively selected. Immunohistochemistry was performed for DLL3 (SC16.65 antibody) and polyomavirus large T-antigen (sc-136172 antibody). Slides were read out for percentage of positive tumor cells. Cox proportional hazards model was applied to assess the association between DLL3 expression and overall survival (OS). A patient with a DLL3-expressing MCC was treated with rovalpituzumab tesirine (Rova-T) in the “other tumor” cohort of NCT02709889 and assessed for response. Results The median H-score of DLL3 expression of 65 patients included was 60 (interquartile range, 30–100). Fifty-eight cases (89%) had ≥1% tumor cells positive for DLL3 expression with any intensity, of which the median DLL3 expression was 50% (interquartile range, 25%–70%). Thirty-four cases (52%) had ≥50% tumor cells positive for DLL3 expression with any intensity. Higher H-score of DLL3 expression was associated with higher polyomavirus nuclear expression (p = .003) when it was dichotomized to negative versus positive. H-score of DLL3 expression did not predict OS of patients with MCC (p = .4) after being adjusted for common clinicopathological factors. A patient treated with Rova-T for refractory metastatic MCC achieved partial response. Conclusions DLL3 overexpression is very common in MCC by immunohistochemistry. The response to treatment suggests that DLL3 expression may have predictive relevance for DLL3-targeting therapies in MCC. Implications for Practice Delta-like protein 3 (DLL3) is being developed as a predictive biomarker to identify patients for treatment with DLL3-targeting agents. Merkel cell carcinoma (MCC) is an aggressive neuroendocrine carcinoma of the skin. It was found that DLL3 overexpression is very common in MCC by immunohistochemistry and significantly associated with Merkel cell polyomavirus expression. Despite the lack of prognostic significance in this cohort, DLL3 expression may have predictive relevance for DLL3-targeting therapies in MCC. The high levels of DLL3 expression in a subset of MCC may potentially be used to select patients to receive DLL3-targeting therapies.

Abstract Purpose: Delta-like protein 3 (DLL3) is being developed as a predictive biomarker to identify small cell lung cancer (SCLC) patients for treatment with the DLL3-targeting antibody-drug conjugate rovalpituzumab tesirine (Rova-T). Merkel cell carcinoma (MCC) is an aggressive neuroendocrine carcinoma of the skin, associated with Merkel cell polyomavirus. Given the neuroendocrine features of SCLC and MCC, we sought to evaluate DLL3 expression, its association with common clinicopathological factors, and its prognostic role in MCC. Methods: A total of 65 formalin-fixed and paraffin-embedded MCC cases were consecutively identified from an institutional biospecimen repository and were cut at 5 µm. Each case was stained for DLL3 protein with SC16.65 mouse monoclonal antibody at 3 µg/mL with the FLEX+ system (DAKO). Slides were then scanned at 20X with AT2 (Leica/Aperio) and read out for percentage of positive tumor cells with 1+, 2+, and 3+ intensity side-by-side with isotype control (IgG2a). Any subcellular staining pattern (membranous, cytoplasmic or punctate) was counted as overall positive. Polyomavirus status was determined by immunohistochemistry (IHC) using an antibody that binds to MCPyV large T-antigen (sc-136172, Santa Cruz Biotechnology, Inc.). A generalized additive model was used to visualize the trend between common clinical factors and overall survival (OS). A multivariable Cox proportional hazards model was applied to assess the association between DLL3 expression and OS. The association between DLL3 expression and other clinicopathological factors was evaluated with median and t tests. Results: A total of 67 patients were included with a median age of 74 years. Thirty-six (55%) had stage I/II disease; 29 (45%) had stage III/IV disease. Thirty-five (52%) patients died from MCC. Among the 65 cases with successful DLL3 stain, the median H-score of DLL3 expression was 60 (interquartile range: 30-100). Fifty-eight cases (89%) had ≥1% tumor cells positive for DLL3 expression with any intensity, of which the median DLL3 expression was 50% (interquartile range: 25-70%). Thirty-four cases (52%) had ≥50% tumor cells positive for DLL3 expression with any intensity. Older age significantly predicted shorter overall survival (p = 0.03). However, higher AJCC stage did not predict shorter OS (p = 0.3). H-score of DLL3 expression was not associated with AJCC stages (p = 0.4). However, higher H-score of DLL3 expression was associated with higher polyomavirus nuclear expression (p = 0.02) when it was dichotomized to 0/1+ and 2+/3+. In a multivariable Cox regression analysis, H-score of DLL3 expression did not predict OS of patients with MCC (p = 0.8). Conclusions: DLL3 overexpression is very common in MCC by IHC. DLL3 expression was significantly associated with Merkel cell polyomavirus expression but was not prognostic for OS in this cohort. The high levels of DLL3 expression in a subset of MCC may potentially be used to select patients to receive Rova-T. Citation Format: Hao Xie, Kumiko Isse, Yan Sun, Johanna Ramoth, Dorothy M. French, Laura R. Saunders, Aaron S. Mansfield. Delta-like protein 3 expression in Merkel cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3171.