Tukysa-Herceptin Approval for Colorectal Cancer Is an ‘Important Breakthrough’ for Chemo-Resistant Disease

The recent Food and Drug Administration (FDA) approval of Tukysa (tucatinib) plus Herceptin (trastuzumab) for previously treated HER2-positive metastatic colorectal cancer provides patients with a chemotherapy-free treatment option with high response rates and manageable side effects, an expert said.

“I think that will be something that patients and family members really appreciate because many of these patients are heavily treated with chemotherapy and are looking for alternatives to that,” said Dr. John H. Strickler, associate professor of medicine at Duke University Medical Center in Durham, North Carolina, in an interview with CURE®. “To achieve this level of benefit with a chemotherapy-free regimen is an important breakthrough for our patients.”

Of note, Strickler added that the FDA approval of Tukysa plus Herceptin affects approximately 3% of patients with metastatic colorectal cancer who have HER2-positive tumors.

From One Size Fits All to Personalized Care

In the past, clinicians typically treated colorectal cancer as one disease, where all patients received the same treatment regardless of the disease’s genetic profile. Recently, biomarker testing has allowed clinicians to learn more about a patient’s disease, to make more informed treatment decisions and to provide patients with more precise treatments.

“This means that we’re able to achieve the same or better results in terms of responses to treatment with fewer side effects,” said Strickler, who was also the lead investigator for the MOUNTAINEER trial, which supported this FDA approval.

The standard of care for patients in the chemotherapy-refractory setting — when the disease does not respond to chemotherapy — had an average response rate of 1% to 2% with a limited survival benefit, Strickler said. In addition, the previous standard of care led to substantial side effects.

Although the Tukysa-Herceptin regimen is a chemotherapy free treatment option, it is associated with some side effects that are manageable, according to Strickler.

“The most common side effect that we noted that’s treatment-related is diarrhea,” Strickler said. “In most cases, this was mild to moderate and well controlled with medications like Imodium (loperamide hydrochloride), so anti-diarrhea medicines. We found that in most cases, the regimen is well tolerated and, in fact, it was very rare for a patient to discontinue this (Tukysa/Herceptin) combination due to a side effect.”

Challenges Moving Forward

Strickler added that he thinks that this regimen will be rapidly adopted in the clinic, especially since Tukysa has already been approved by the FDA for the treatment of breast cancer. Despite this, Strickler thinks that the challenge lies in testing patients for HER2 amplification or overexpression so that clinicians know whether a patient is eligible for this treatment. Biomarker testing is currently standard of care, but many patients are still not receiving this testing.

“We don’t know all the reasons for (patients not receiving biomarker testing), but one of the barriers we faced is that oftentimes, the assays rely on new technology that can be expensive,” Strickler explained. “Sometimes insurance does not reimburse for the testing, which can make it difficult for physicians to order it and can create a burden for patients.”

Strickler said he and other clinicians are advocating that all patients should receive biomarker testing.

Another unmet need that persists in the previously treated HER2-positive metastatic colorectal cancer is a treatment option for patients with a RAS mutation (ie, KRAS and NRAS) and HER2-positive disease

“We’re looking forward to seeing more data from other novel therapies that could potentially reach that group of patients who are not impacted by this approval,” Strickler said.

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