PD-1 Blockade with Pembrolizumab in Advanced Merkel-Cell Carcinoma

Abstract

Background: Merkel-cell carcinoma is an aggressive skin cancer that is linked to exposure to ultraviolet light and the Merkel-cell polyomavirus (MCPyV). Advanced Merkel-cell carcinoma often responds to chemotherapy, but responses are transient. Blocking the programmed death 1 (PD-1) immune inhibitory pathway is of interest, because these tumors often express PD-L1, and MCPyV-specific T cells express PD-1.

Methods: In this multicenter, phase 2, noncontrolled study, we assigned adults with advanced Merkel-cell carcinoma who had received no previous systemic therapy to receive pembrolizumab (anti-PD-1) at a dose of 2 mg per kilogram of body weight every 3 weeks. The primary end point was the objective response rate according to Response Evaluation Criteria in Solid Tumors, version 1.1. Efficacy was correlated with tumor viral status, as assessed by serologic and immunohistochemical testing.

Results: A total of 26 patients received at least one dose of pembrolizumab. The objective response rate among the 25 patients with at least one evaluation during treatment was 56% (95% confidence interval [CI], 35 to 76); 4 patients had a complete response, and 10 had a partial response. With a median follow-up of 33 weeks (range, 7 to 53), relapses occurred in 2 of the 14 patients who had had a response (14%). The response duration ranged from at least 2.2 months to at least 9.7 months. The rate of progression-free survival at 6 months was 67% (95% CI, 49 to 86). A total of 17 of the 26 patients (65%) had virus-positive tumors. The response rate was 62% among patients with MCPyV-positive tumors (10 of 16 patients) and 44% among those with virus-negative tumors (4 of 9 patients). Drug-related grade 3 or 4 adverse events occurred in 15% of the patients.

Conclusions: In this study, first-line therapy with pembrolizumab in patients with advanced Merkel-cell carcinoma was associated with an objective response rate of 56%. Responses were observed in patients with virus-positive tumors and those with virus-negative tumors. (Funded by the National Cancer Institute and Merck; ClinicalTrials.gov number, NCT02267603.).

Figures

Figure 1. Clinical Characteristics of Tumor Response to Pembrolizumab in Patients with Merkel-Cell Carcinoma

Panel A shows the maximum percent change from baseline in the sum of the longest diameters of target lesions in the 24 patients who underwent radiologic evaluation after treatment initiation. Viral status refers to whether patients had tumors that were positive or negative for the Merkel-cell polyomavirus (MCPyV). Horizontal dashed lines indicate criteria in the Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1, for partial response (≥30% decrease in the sum of the longest diameters of target lesions, with the assumption of no new lesions) and progressive disease (≥20% increase in target-lesion diameters). Data from 2 of the 26 patients are not shown: one had radiographic evidence of disease progression with new lesions, without radiographic evaluation of target lesions, and thus discontinued therapy; the other had not yet undergone radiologic evaluation after initiating pembrolizumab therapy, as of the date of analysis. Panel B shows the kinetics of change in target-lesion diameters over time during pembrolizumab therapy. Rapid and durable reductions in target-lesion diameters were observed in most patients. Two patients with confirmed responses (1 with a partial response and 1 with a complete response) subsequently had progression in nontarget lesions, which are not represented here. Panel C shows the characteristics of 16 patients who initially had evidence of response according to RECIST, version 1.1. Each horizontal bar represents 1 patient. Most responses were observed at the first tumor assessment (approximately 12 weeks after treatment initiation), and 13 of the 16 initial responses (81%) were ongoing at the time of analysis. A total of 14 patients had a confirmed response (2 of whom later had progressive disease); in addition, 1 patient with an unconfirmed partial response continues to receive therapy (bottom bar), and one patient with a transient partial response (i.e., not confirmed by follow-up computed tomographic scanning) subsequently had progressive disease (next-to-bottom bar).

Figure 2. Kaplan–Meier Curve Showing Progression-free Survival among 26 Patients with Merkel-Cell Carcinoma Who Received Pembrolizumab

Progression-free survival was measured from treatment initiation to disease progression or death, whichever occurred first. Data from patients without an event were censored at the last date of disease assessment (tick marks). The estimated rate of progression-free survival at 6 months was 67% (95% confidence interval [CI], 49 to 86). The median progression-free survival was 9 months (95% CI, 5 months to not reached). As of February 12, 2016, a total of 11 events of disease progression or death had occurred.

Figure 3 (facing page). Response to Pembrolizumab in a Patient with Stage IV Merkel-Cell Carcinoma

This 69-year-old woman received a diagnosis of a primary cutaneous lesion on the right knee and was treated with wide local excision, sentinel lymph-node biopsy, and inguinal lymph-node dissection in November 2013. Recurrent Merkel-cell carcinoma developed in September 2014, with a pelvic mass measuring 11 cm by 7 cm by 14 cm, which was associated with worsening lymphedema and moderate-to-severe right hydroureterone-phrosis requiring a ureteral stent. The patient received radiation therapy to the pelvic mass but in January 2015 was found to have new peritoneal and lymph-node metastases (Panel A, red arrows), as well as several subcutaneous metastases on the right thigh and just below the site of excision of the primary tumor (Panel B; red arrow indicates the site of previous excision of the primary tumor, just below the knee). As shown, these metastatic sites regressed rapidly during anti–programmed death 1 (PD-1) therapy. Also shown are the results of pathological analysis of the primary tumor (Panel C, left) and adjacent post-treatment subcutaneous metastasis (Panel C, right) with multispectral immunohistochemical analysis. Orange indicates Merkel carcinoma cells expressing neuron-specific enolase, yellow CD8+ T cells, red CD68+ macrophages, white PD-1, green the PD-1 ligand PD-L1, and blue nuclear DNA stained with 4′,6-diamidino-2-phenylindole (DAPI). Analysis of the archival biopsy specimen shows an immune infiltrate that is most intense at the tumor–stromal interface, including CD68+ macrophages and CD8+ T cells infiltrating the tumor parenchyma. PD-1 is expressed on 56% of CD8 cells in this microscopic field. PD-L1 is expressed on tumor cells (10% of tumor cells in this field, blue arrows) and macrophages (43% of macrophages in this field, red arrows) and is seen immediately adjacent to PD-1+ lymphocytes. Analysis of the post-treatment biopsy specimen shows a diffuse immune-phagocytic infiltrate and no evidence of residual tumor. The immune infiltrate includes CD68+ macrophages and CD8+ T cells, with an early lymphoid aggregate (white star) where PD-1 and PD-L1 expression is observed.

Figure 4. Expression of PD-1 and PD-L1 in Pretreatment Tumor Specimens, Detected by Immunohistochemical Testing

Tumor-cell expression of PD-L1 (≥1% of tumor cells) was observed in 56% of tumors (14 of 25). Panels A and B show the results of chromogenic staining for PD-L1 (brown), immunofluorescent staining for PD-1 (green), and DAPI staining for nuclear DNA (blue). In most PD-L1+ tumors (11 of 14; 79%), PD-L1 expression was observed only in association with PD-1+ lymphoid infiltrates, typical of an “adaptive immune resistance” pattern (Panel A). One tumor (Panel B) showed broad, constitutive tumor-cell expression of PD-L1 that was independent of lymphoid infiltrates, with only a small focal area (not shown) of adaptive PD-L1 expression at the tumor periphery. The remaining two PD-L1+ tumors showed geographic areas of both constitutive and adaptive patterns of PD-L1 expression (not shown). As shown in Panel C, no significant association was observed between pretreatment tumor PD-L1 expression and response to pembrolizumab according to RECIST, version 1.1, among the 23 patients included in this analysis (P = 0.61 by unconditional exact test on a two-by-two contingency table). Of the 3 patients who were not included in this analysis, 1 had not yet undergone a response evaluation, 1 had an unconfirmed response, and 1 had a stained tumor specimen that was technically inadequate. Samples were considered to be PD-L1–positive if at least 1% of tumor cells expressed PD-L1. Panel D shows the correlation of tumor MCPyV status with PD-L1 expression. A total of 71% of virus-positive tumors also showed PD-L1 expression on tumor cells; in contrast, only 25% of virus-negative tumors were positive for PD-L1 (P = 0.049 by unconditional exact test). Only 25 of the 26 patients were included in this analysis, because 1 patient had a stained tumor specimen that was technically inadequate.