Had My Patient Come In Today, We May Have Had Other Options

Joan H. Schiller, MD

October 05, 2022

Decades ago I saw a patient with non–small cell lung cancer (NSCLC) whose tumor was sent out for next-generation sequencing only to find a HER2 mutation. What to do? Had my patient come in today, we may have had other options.

Multiple studies have shown that trastuzumab (Herceptin, Genentech), as assessed by HER2 overexpression or amplification, has been shown to have essentially no efficacy benefit in NSCLC alone or in combination with chemotherapy. In fact, a randomized, phase 2 study of gemcitabine-cisplatin with or without trastuzumab in HER2 mutation–positive NSCLC essentially showed no difference between gemcitabine-cisplatin or gemcitabine-cisplatin with trastuzumab.

NSCLC has become the poster child for targeted therapies. After all, NSCLC makes up about 85% of all lung cancer cases, some of which are driven by gene mutations or other genetic abnormalities like translocation, fusion, or amplification. Seven of these genetic alterations have Food and Drug Administration–approved targeted drugs: EGFR, ALK, ROS1, BRAF V6006, RET, KRAS, MET, and NTRK fusions. And, now we have a new one: HER2.

In August, the FDA granted accelerated approval of trastuzumab deruxtecan (T-DXd) (Enhertu, Daiichi Sankyo) for the second-line treatment of NSCLC patients with HER alterations. T-DXd is a humanized anti-HER antibody linked to a topoisomerase 1 inhibitor. When given intravenously, the antibody portion of the molecule binds to cells with a mutated HER2 on the surface. The molecule is taken up by the cancer cell and the linker between the antibody and the chemotherapy drug is broken, so the drug will be delivered very specifically only to cancer cells that have a mutated HER2. In theory, they will only target cells with HER alterations and thus should have less toxicity.

Unlike other driver mutations, HER mutations are relatively rare. Roughly 3% of nonsquamous NSCLC tumors carry mutations in the HER2 gene, and they are associated with female sex, never-smokers, and a poor prognosis. Accelerated approved by the FDA was based on data from the DESTINY-Lung 02 phase 2 trial. An interim efficacy analysis of this trial reported an overall response rate to trastuzumab deruxtecan (at 5.4 mg/kg every 3 weeks) of 57.7% in 52 patients. Median duration of response was 8.7 months. Data are also available from the DESTINY-Lung-01 clinical trial, published in the New England Journal of Medicine, in which 91 patients with metastatic HER2-mutant NSCLC that was refractory to standard treatment were treated with T-DXd (at 6.4 mg/kg every 3 weeks). The investigators reported a 55% objective response rate, a median duration of response of 9.3 months, a median progression-free survival (PFS) of 8.2 months, and a median overall survival of almost 18 months.

Companion Tests

Biomarker testing is obviously a must in these cases. The FDA-approved companion diagnostic tests to detect HER2 mutations: Life Companion tests, Technologies Corporation's Oncomine Dx Target Test for use in lung tissue, and Guardant Health's Guardant360 CDx for use on plasma samples. The agency notes that, if no mutation is detected in a plasma specimen, the tumor tissue should be tested.

Other Approvals

T-DXd is also approved for advanced breast and gastric patients who are HER-2 positive. Of note, the majority of HER2-positive NSCLC have HER2 mutations, whereas the majority of HER2-positive breast and gastric cancers have HER2 amplification (increased copy number) or overexpression (increased protein expression).

T-DXd is approved for unresectable or metastatic HER2-positive breast cancer patients who have received a prior anti-HER2–based regimen in the metastatic setting, or in the neoadjuvant or adjuvant setting and have developed disease recurrence during or within 6 months of completing therapy. DESTINY-Breast01 enrolled breast cancer patients who had received two or more prior anti-HER2 therapies in the metastatic setting, and reported a response rate of 60.3% with a median duration of response of 14.8 months.

For patients with locally advanced or metastatic HER2-positive gastric cancer who have received two or more prior therapies, including a trastuzumab-based regimen, approval was based on a randomized, phase 3 study comparing 6.4 mg/kg of T-DXd with physician's choice – either irinotecan or paclitaxel. Overall survival was 12.5 months in the T-DXd arm, compared with 8.4 months in the irinotecan or paclitaxel arm (hazard ratio, 0.59). Response rates were 40.5% and 11.3%, respectively. Median PFS was 5.6 months in the T-DXd arm, compared with a median PFS of 3.5 months in the chemotherapy arm.

Trastuzumab Emtansine vs Trastuzumab Deruxtecan

Trastuzumab emtansine (T-DM1, ado-trastuzumab emtansine, Kadcyla) is another antibody-drug conjugate consisting of the humanized monoclonal antibody trastuzumab covalently linked to the antimicrotubule agent DM1. It is also approved for advanced breast cancer patients with HER2-positive disease. Although no studies comparing T-DXd with trastuzumab emtansine have been conducted in lung cancer patients, a randomized, phase 3 trial in patients with HER2-positive advanced breast cancer comparing the two reported an overall response rate of 79.7% of the patients who received trastuzumab deruxtecan and 34.2% of those who received trastuzumab emtansine. Drug-related interstitial lung disease (ILD) occurred in 10.5% of the patients in the trastuzumab deruxtecan group and in 1.9% of those in the trastuzumab emtansine group; at 12 months, 75.8% of the patients in the trastuzumab deruxtecan were alive without progression, compared with 34.1% of those receiving trastuzumab emtansine.


In DESTINY-Lung01, ILD occurred in 26% of patients and resulted in death in two patients. Increased rates of ILD were more commonly observed at higher dose levels. Of 491 patients with unresectable or metastatic HER2-positive breast cancer treated with 5.4 mg/kg of T-TDx, ILD occurred in 13% of patients. Fatal outcomes caused by ILD and/or pneumonitis occurred in 1.4% of patients. Median time to first onset was 5.5 months (range, 1.1-20.8 months). In DESTINY-Gastric01, of the 125 patients with locally advanced or metastatic HER2-positive gastric or gastroesophageal junction adenocarcinoma treated with 6.4 mg/kg, T-DXd ILD occurred in 10% of patients. Median time to first onset was 2.8 months (range, 1.2-21.0 months).

Chemotherapy-Like Adverse Effects

Other adverse events are more typically seen with cytotoxic agents and are presumably related to the release of the topoisomerase inhibitor into the blood stream. Although common (occurring in 97% of patients), these adverse events are generally mild (grade 1 or 2). Nausea was reported in about two-thirds of patients. Other side effects occurring in 20% or more of patients included vomiting, decreased appetite, alopecia, and constipation and diarrhea, musculoskeletal pain, and respiratory infections. Laboratory abnormalities occurred in 20% or more of patients included myelosuppression, increased AST, ALT, alkaline phosphatase, and hypokalemia (28%). Grade 3 or higher drug-related adverse events were observed in 46% of patients, with the most common being neutropenia and anemia which was observed in 19% and 10% of patients in the DESTINY-LUNG-01 trial.

Schiller is a medical oncologist and founding member of Oncologists United for Climate and Health. She is a former board member of the International Association for the Study of Lung Cancer and a current board member of the Lung Cancer Research Foundation.

This article originally appeared on, part of the Medscape Professional Network.


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