In the phase II SUMMIT clinical trial, the likelihood that a patient’s cancer responded to the investigational pan-HER–targeted therapeutic neratinib was influenced by both the cancer type and the identity of the gene mutation present in the cancer, according to results presented here at the AACR Annual Meeting 2017.

“Mutations in the HER2 and HER3 genes are found at relatively low frequency in a variety of types of cancer,” said David M. Hyman, MD, director of Developmental Therapeutics at Memorial Sloan Kettering Cancer Center in New York. "We designed a clinical trial to validate whether these mutations are rational therapeutic targets and whether the investigational therapeutic neratinib, which targets members of the HER family, has anticancer activity."

"By enrolling patients with a wide variety of cancer types harbouring many different mutations, we have assembled a data set large enough to unravel the complex relationship between cancer type, mutation identity, and susceptibility to pan-HER inhibition,” continued Hyman. “It appears that there is not a binary relationship and that both cancer type and mutation identity are important.”

At interim data cutoff, which was December 16, 2016, 141 patients with cancers harbouring HER2 or HER3 mutations had received neratinib as part of the clinical trial.

Among these patients were 21 unique types of cancer, 30 unique HER2 gene mutations, and 12 HER3 gene mutations.

The most common types of cancer were bladder, breast, colorectal, and non–small cell lung cancer; the most common HER2 gene mutations included S310, L755, A755_G776insYVMA, and V777.

When looking at the data by cancer type, the best response rate was seen for breast cancer; biliary and cervical cancers showed an intermediate response rate; there were no responses seen for colorectal cancer.

“Analysing the data in this way shows that cancer type is important, but it is not the whole answer; for example, there were no responses for any cancer type harbouring a HER3 mutation, and when considering individual cancer types, different HER2 mutations had different sensitivity to neratinib,” said Hyman.

“We will present detailed data defining response rates by type of cancer and mutation identity at the meeting,” added Hyman. “The take-home message at this point is that there are areas of promise, but we will likely need to combine pan-HER inhibition with other treatment modalities, such as chemotherapy or antihormone therapy, in order to obtain practice-changing response rates and durability of response. This is not surprising given that the FDA-approved HER2- targeted therapeutics trastuzumab, pertuzumab, and lapatinib are used in combination with chemotherapy for the treatment of breast cancer.”

According to Hyman, the main limitation of the study is that even though it has enrolled a comparatively large number of patients for a phase II clinical trial selecting a rare molecular subtype, they have still not saturated enrollment with patients harbouring each combination of cancer type and specific mutation.

“Despite this, we have learned a huge amount from the trial,” said Hyman. “There have been reports on the responsiveness of HER2-mutant cancers to off-label use of FDA-approved HER2- targeted therapeutics, but this study provides a rigorous analysis of the many variables that are involved and will provide the most definitive data to guide the clinical development of HER family–targeted therapeutics in HER2/3 mutant tumours.”

Source: AACR 2017