Patients with metastatic breast cancer who carry rare mutations identified by circulat­ing tumor DNA responded to matched targeted therapies, according to results of the plasmaMATCH trial presented during the 2019 San Antonio Breast Cancer Symposium. Specifically, patients with HER2 mutations responded to neratinib and patients with AKT1 mutations responded to capivasertib.
Nicholas Turner, PhD, MA, MRCP
Patients with metastatic breast cancer who carry rare mutations identified by circulat­ing tumor DNA (ctDNA) responded to matched targeted therapies, according to results of the plasmaMATCH trial (NCT03182634) presented during the 2019 San Antonio Breast Cancer Symposium.1Specifically, patients with HER2 mutations responded to neratinib (Nerlynx) and patients withAKT1mutations responded to capivasertib.
The benefit of ctDNA is its ability to provide tumor genotyping information in a noninvasive, simple, and efficient method that can aid making a diagnosis and prognosis and guide treatment.2Using ctDNA may pro­vide a more current assessment of the genetic profile of advanced breast cancer compared with analysis of the primary tumor. Historically, ctDNA has been used in solid malignancies to detect actionable driver mutations, monitor treatment response, detect recurrence, identify resistance mechanisms, and prognosticate outcome.
The study’s lead author,Nicholas Turner, PhD, MA, MRCP, of The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, both in London, England, said during the presentation that the plasmaMATCH trial was designed to assess the clinical utility of using ctDNA testing to select patients for targeted therapies.
"Our team wanted to solve the issue of genotyping breast cancer tumors without having to perform multiple biopsies,” Turner said in a statement.3Because mutations can change after treatment or when cancer metastasizes, it is important to develop methods to easily identify genetic mutations. Further, it is not always possible to take addi­tional biopsies from patients with advanced disease.
Between December 2016 and April 2019, 1044 patients with metastatic or locally recurrent breast cancer were registered for the trial. Of 1033 patients screened, 142 entered into 4 parallel treatment cohorts with therapies matched to mutations that were identified through ctDNA testing.
The investigators reported that ctDNA testing was con­ducted prospectively using digital droplet polymerase chain reaction (ddPCR) in all patients. Guardant360 was used prospectively for error-corrected sequencing during recruitment. Sequencing from an advanced dis­ease biopsy was conducted retrospectively and did not influence cohort entry, according to investigators.
At baseline, median age at registration was 56 years (range, 49-65) and 146 patients (14%) had metastatic disease at diagnosis. Thirty-six percent (n = 382) of patients had received ≥2 lines of chemotherapy; 8% (n = 89), a CDK4/6 inhibitor; 65% (n = 685), endo­crine therapy; and 69% (n = 727), chemotherapy.
Mutation frequencies were reported using ddPCR as follows:ESR1, 27.7%;HER2, 2.7%;AKT1, 4.2%. Patients in cohort A had theESR1mutation; all were hormone receptor (HR) positive and 3 (4%) were HER2-positive. In cohort B, patients had theHER2mutation, with 86% HR-positive and 14% HER2-positive. For cohort C, patients had theAKT1mutation with estrogen receptor (ER)positive breast can­cer; all were HR positive and 1 (6%) was also HER2-positive. In cohort D, patients had theAKT1mutation in ER-negative breast cancer or thePTEN-inactivating mutation; 13 (68%) were HR-positive, and all patients were HER2- negative (TABLE 1).1Results for cohort E, which was designated for patients with no actionable mutations and triple-negative breast cancer, will be reported separately, Turner said.
Cohort A (n = 74) received fulvestrant 500 mg intramuscularly on days 1, 8, and 15 of cycle 1 and days 1 and 15 of cycle 2. Patients in cohort B (n = 20) received neratinib 240 mg orally on a continuous schedule starting day 1 of cycle 1, and patients with ER-positive breast cancer received fulvestrant 500 mg intramus­cularly on days 1 and 15 of cycle 1 and in cycle 2 onward after day 1. Patients in cohort C (n = 18) received capiva­sertib 400 mg orally twice a day on a 7-day schedule of 4 days on treatment followed by 3 days off and fulvestrant 500 mg intra­muscularly during days 1 and 15 of cycle 1 and in cycle 2 onward after day 1. Patients in cohort D (n = 19) received capivasertib 480 mg orally twice a day on a 7-day schedule of 4 days on treatment followed by 3 days off. In cohort E, patients received capivasertib 160 mg once daily on days 1 to 7 of each cycle and olaparib (Lynparza) 300 mg twice daily on a continuous schedule starting with cycle 1 on day 1.
The primary end point for cohorts A through D was confirmed objective response rate by RECIST 1.1. Secondary end points included clinical benefit rate, progression-free survival (PFS), and safety and frequency of mutations identified in ctDNA screening.
The investigators reported a high level of individual gene-level agreement between ctDNA digital PCR and sequencing results (95.5%-99.4%; κ _= 0.89-0.93). When comparing the patients’ tumor samples with the findings from ctDNA testing, the investigators found that the ctDNA assay had an overall sensitivity of 93%.
The investigators noted that Guardant360 identified over 35% morePIK3CAmutations that can be targeted by therapies approved by the FDA. The assay also detected significantly moreESR1mutations and found previously undetected microsatellite instability andERBB2mutations.
Predefined efficacy criteria were met in cohorts B (neratinib forHER2mutations) and C (capivasertib forAKTmutations), with explor­atory analysis of cohort D identifying activity of capivasertib inAKT1mutations (TABLE 2). Efficacy criteria were not met in cohort A (extended-dose fulvestrant forESR1mutations).
Specifically, patients in cohort A had an 8.1% response, which was below the threshold for inferred efficacy. In cohort B, patients with theHER2mutation had a response rate of 25.0%, demon­strating inferred efficacy. In cohort C, 22.2% of patients demonstrated a response; in D, 10.5% had a response, which was below the efficacy threshold. In this cohort, an exploratory analysis of patients with anAKT1mutation had a response rate of 33.3% (2 of 6 patients), which did meet efficacy levels.
Adverse events were consistent with prior reports, with extended-dose fulvestrant well tolerated, according to the investigators. “This is a huge step in terms of making decisions in the clinic, particularly for those women with advanced breast cancer who could quickly be put on new targeted treatments matched to their cancer if [the disease] evolves to become drug resistant,” Turner said.
The investigators say the results suggest a robust way of identifying rare subtypes of breast cancer and could replace the more invasive methods of analyzing breast tumors.
“We now have confirmed that blood tests can quickly give us a bigger picture of the mutations that are present within multiple tumors throughout the study,” concluded Turner.