From the Journals

Dramatic response from pembrolizumab in patient with Lynch syndrome



A woman with two distinct primary tumors achieved complete regression of both after pembrolizumab therapy, investigators report.

This is the first documented instance of a checkpoint inhibitor leading to this kind of simultaneous regression, reported Benjamin Musher, MD, of Baylor College of Medicine, Houston, and his coauthors.

The patient was a 55-year-old woman with a family history of gastric, uterine, and colon cancer. After presenting with weight loss, fatigue, and abdominal pain, colonoscopy showed a 5-cm mucosal lesion. A subsequent PET-CT scan revealed a 12-cm hepatic mass with multiple other liver masses, and bulky lymph nodes nearby. Site biopsies showed two primary cancer types: colonic adenocarcinoma and intrahepatic cholangiocarcinoma.

“Additional staining ... for proteins that repair mismatched DNA showed an absence of MLH1 expression. Sequencing of the patient’s DNA revealed a deleterious mutation in MLH1, which confirmed that Lynch syndrome caused both types of cancer,” the authors wrote in Annals of Internal Medicine.

Lynch syndrome (also called hereditary nonpolyposis colorectal cancer), is an autosomal dominant condition that incurs a high risk of colorectal, pancreatic, bile duct, ovarian, gastric, and uterine cancer. Patients may present with more than one type of cancer simultaneously, as occurred in this case study.

Following diagnosis, the patient started pembrolizumab monotherapy (200 mg IV Q3W). After 16 months the tumors were undetectable by colonoscopy or PET-CT; 2 months later the patient was free of cancer symptoms.

“To our knowledge, our case report is the first to document complete regression of 2 simultaneous types of cancer after treatment with an immune checkpoint inhibitor,” the authors wrote.

But why the dramatic response?

“The types of cancer that develop because of a mismatch repair deficiency contain more mutations than most other kinds of cancer,” the authors explained. These highly mutated cells are recognized by the host immune system, but responses are limited, in part, by programmed cell death proteins. “These events make checkpoint inhibition an attractive and potentially effective treatment for mismatch repair deficient cancer.

“We believe that this case emphasizes the importance of eliciting a thorough family history in patients with cancer and considering the presence of multiple types of primary cancer in a patient with an extensive family history of cancer,” the authors concluded. “It also shows the value of identifying mismatch repair deficiency, [in which] immunotherapy can yield dramatic and durable benefit.”

Dr. Musher reported compensation from LOKON pharmaceuticals.

SOURCE: Musher et al. Ann Intern Med. 2018 Sep 24. doi: 10.7326/L18-0360.

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