Expert Highlights Assay to Determine Patients With Lung, Gastrointestinal Cancers to Receive Pembrolizumab

The PD-L1 immunohistochemistry 22C3 pharmDx can be an aid in identifying patients with non–small cell lung cancer and gastrointestinal cancers who are eligible for pembrolizumab (Keytruda) monotherapy.

Lawrence M. Weiss, MD

The PD-L1 immunohistochemistry (IHC) 22C3 pharmDx can be an aid in identifying patients with non—small cell lung cancer (NSCLC) and gastrointestinal cancers who are eligible for pembrolizumab (Keytruda) monotherapy, according to Lawrence M. Weiss, MD.

This assay is approved by the FDA as a companion diagnostic for pembrolizumab in NSCLC and gastric/gastroesophageal junction (GEJ) adenocarcinoma.

“This is a specific FDA-approved assay using a specific antibody clone, 22C3. There are other antibody clones available, but for this specific FDA-approved test, it involves 22C3 using the EnVision FLEX Visualization System on the Autostainer Link 48,” Weiss said in a presentation during the 2nd Annual International Congress on Oncology Pathology.

“This is a proprietary platform for one of the immunohistochemical vendors, and both of those components are important to the FDA-approved test. You can’t use a different clone with that machine; you can’t use that clone with a different machine. It also has to follow strict guidelines.”

In his presentation, Weiss, medical director and director of pathology services at NeoGenomics, reviewed how to test for PD-L1 expression and microsatellite instability (MSI)/mismatch repair deficient (dMMR) status, how to score PD-L1 expression based on tumor biology, and how the biomarker can inform treatment decisions.

Pembrolizumab is indicated as a first-line treatment for patients with metastatic NSCLC who whose tumors have ≥50% PD-L1 expression with no EGFR or ALK abnormalities, a second-line or greater treatment for metastatic NSCLC with PD-L1 expression, recurrent locally advanced or metastatic gastric/GEJ adenocarcinoma that is PD-L1 positive, and advanced MSI-H or dMMR solid tumors. Weiss noted this is not a full list of the indications for pembrolizumab, which also includes a frontline therapy in combination with carboplatin/pemetrexed for patients with metastatic nonsquamous NSCLC.

The NCCN guidelines recommend PD-L1 expression testing as part of the diagnostic evaluation of patients for their metastatic NSCLC treatment. All of these patients should be tested for PD-L1 expression, as testing at diagnosis can help inform treatment decisions, Weiss said.

“We recommend that all patients with metastatic squamous and non-=squamous NSCLC should be tested for PD-L1 [expression],” said Weiss. “Many people just test all lung cancers knowing that many are or will become metastatic or clinically recurrent at some point. Obviously, testing for PD-L1 at diagnosis can inform treatment decisions, which may or may not include Keytruda.”

Calculation for PD-L1 score includes viable tumor cells and partial or complete membrane staining at any intensity. The score does not include cytoplasmic staining, immune cells, normal cells, or necrotic cells. The score is broken down into 3 groups: no PD-L1 expression (tumor proportion score [TPS] <1%), PD-L1 expression (TPS ≥1%), and high PD-L1 expression (TPS ≥50%).

“Greater than 50% makes you eligible for the first-line therapy, and greater than 1% makes you eligible for the second-line therapy,” Weiss explained.

He noted that 66% (1475/2222) of patients in the KEYNOTE-010 trial had PD-L1 expression,1 and 30% (500/1653) of patients in the KEYNOTE-024 trial had high PD-L1 expression.2 Both of these trials evaluated pembrolizumab compared with chemotherapy in patients with metastatic NSCLC.

Among a total 2799 patients treated with pembrolizumab across several studies, the most common immune-mediated all-grade adverse events included hypothyroidism (8.5%), hyperthyroidism (3.4%), and pneumonitis (3.4%).

NCCN guidelines also recommend PD-L1 testing in metastatic gastric/GEJ adenocarcinoma.

PD-L1 score for gastric or GEJ adenocarcinoma includes viable tumor cells with convincing partial or complete membrane staining at any intensity, and lymphocytes and macrophages (mononuclear inflammatory cells, MICs) within tumor nests. PD-L1 status does not include normal cells, tumor cells with cytoplasmic staining, necrotic cells, adenoma, dysplasia, carcinoma in situ, MICs associated with adenoma, dysplasia, or carcinoma in situ or associated with ulcers or chronic gastritis, neutrophils, eosinophils, or plasma cells.

A combined positive score (CPS) <1 is considered no PD-L1 expression while CPS ≥1 is considered PD-L1 expression.

In the KEYNOTE-059 trial of pembrolizumab in gastric/GEJ adenocarcinoma, 55% (143/259) of patients had PD-L1 expression, Weiss noted.

“As a reflection, NCCN guidelines now recommend PD-L1 testing in metastatic gastric or gastroesophageal junction adenocarcinoma,” he said.

In May 2017, the FDA approved pembrolizumab for the treatment of adult and pediatric patients with unresectable or metastatic MSI-H or dMMR solid tumors that have progressed following prior treatment and have no satisfactory alternative treatment options, or, specifically, patients with colorectal cancer that has progressed following treatment with fluoropyrimidine, oxaliplatin, and irinotecan.

“In contrast to PD-L1, where we had an FDA-prescribed test where you have to follow the test exactly, or else you’re not following the proper FDA guidelines, the FDA approval said you can determine either dMMR or MSI status and use any laboratory-developed test. These are tests that have not been approved by the FDA but are validated within the labs that are offering the tests,” Weiss said.

There are 3 widely available laboratory-developed tests that can be used to determine MSI/dMMR status in advanced solid cancers—IHC, polymerase chain reaction, and next-generation sequencing.

Patients who are identified as dMMR or MSI-high (MSI-H) in one of these tests are eligible for treatment with pembrolizumab. dMMR is defined as loss of MLH1, MSH2, MSH6, and/or PMS2 expression is detected. MSI-H is defined as ≥2 altered microsatellite sequences.

“If MSI-H is found, or if there are deficiencies in the MMR proteins, these are results indicating that patients may be eligible for [pembrolizumab],” Weiss said.


  1. Herbst RS, Baas P, Kim D-W, et al. Pembrolizumab versus docetaxel for previously treated, PD-L1-positive, advanced non-small-cell lung cancer (KEYNOTE-010): a randomised controlled trial. Lancet Oncol. 2016;387(10027):1540-1550. doi: 10.1016/S0140-6736(15)01281-7.
  2. Reck M, Rodgriguez-Abreu D, Robinson AG, et al. Pembrolizumab versus chemotherapy for PD-L1—positive non–small-cell lung cancer. N Eng J Med. 2016;375(19):1823-1833. doi: 10.1056/NEJMoa1606774.
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