2018 Update on gynecologic cancer
Gynecologic malignancies remain a major cause of morbidity and mortality. In this article: latest cervical cancer screening recommendations from the USPSTF, and 2 endometrial cancer news items, on SLN biopsy and PD-1 blockade immunotherapy.
Immunotherapy for gynecologic cancers
Le DT, Durham JN, Smith KN, et al. Mismatch repair deficiency predicts response of solid tumors to PD-1 blockade. Science. 2017;357(6349):409-413.
In oncology, precision medicine is rapidly becoming a standard treatment approach. Therapies are being used to target specific genetic alterations in tumors. In cancer immunotherapy, the immune system is being used to facilitate clearance of cancer cells.
,The most common mechanism of action of clinically used immunotherapeutic agents is blockade of programmed cell death protein 1 (PD-1), a lymphocyte receptor that prevents the immune system from targeting the body's own cells.7 Cancers that have mutations in the DNA mismatch repair (MMR) proteins display microsatellite instability (MSI) and produce high levels of abnormal proteins.8 These abnormal proteins serve as tumor antigens that can be targeted by the body's normal immune system.
In May 2017, the US Food and Drug Administration (FDA) granted accelerated approval of the PD-1 blocking antibody pembrolizumab for the treatment of unresectable or metastatic MSI-high (MSI-H) or MMR-deficient solid tumors.9 The approval was based on data from 149 patients treated in 5 studies that demonstrated a response rate of 39.6%, including responses that lasted at least 6 months in 78% of participants. This was the first ever cancer drug that received FDA approval based on a tumor's biomarker profile without regard to the site of origin. I describe the results of a study by Le and colleagues that examines the possible role of immunotherapy in a variety of solid tumors in this section.
Details of the study
This study examined the clinical efficacy of PD-1 blockade in 86 patients with advanced, MMR-deficient tumors from 12 different sites. Endometrial cancer was the second most frequent primary tumor site in 17% of patients. Within the cohort, the overall objective response rate was 53%, which included 21% of patients with complete radiographic response (no imaging evidence of cancer). Disease control, either complete or partial response or stable disease, was achieved in 77% of patients. After a median follow-up of 12.5 months, neither the median progression-free survival (PFS) nor median overall survival had been reached. The authors estimated that 2-year overall survival was 64%, substantially higher than expected for patients with advanced solid tumors.
Le and colleagues also performed several in vivo laboratory experiments to explore the mechanisms by which patients responded. In addition, they used sequencing to determine the prevalence of MMR deficiency in 12,019 cancer samples that included 32 distinct tumor types (FIGURE). Endometrial cancer had the highest frequency of MMR deficiency (17%). Four percent of cervical cancers and less than 2% of ovarian cancers were MMR-deficient.
The promise of immunotherapy for endometrial cancer. This study's data and other emerging data have important implications for women with gynecologic cancer, particularly endometrial cancer. First, given the frequency of MMR mutations among women with endometrial cancer, MMR testing should be strongly considered for these patients. Many institutions have protocols for reflex testing with immunohistochemistry for women with endometrial cancer. For women with positive test results, germline sequencing can be performed to determine if they have an inherited MMR deficiency, Lynch syndrome. Presence of an MMR deficiency is an important factor in cancer screening and potential treatment.
Second, the impressive results of PD-1 blockade in patients with MMR-deficient tumors suggest that this treatment strategy may be important for women with recurrent or metastatic endometrial cancer. The ideal timing of immunotherapy for women with endometrial cancer is an area of active ongoing study.
Immunotherapy with PD-1 blockade is an important treatment strategy for women with MMR-deficient or MSI-H gynecologic cancers.
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