Testing for feasibility
The aim of the current study was to assess the feasibility and potential usefulness of sequencing DNA and RNA from clinical tumor specimens from patients who had experienced unusually profound or durable responses to systemic therapy.
Its main feasibility goal was to identify at least 100 cases involving exceptional responders whose cases could be analyzed in less than 3 years.
An exceptional patient was defined as one who had experienced a complete response to one or more drugs in which complete responses were seen in fewer than 10% of patients who received similar treatment; or a partial response lasting at least 6 months in which such a response is seen in fewer than 10% of patients who receive similar treatment; or a complete or partial response of a duration that is three times the median response duration represented in the literature for the treatment.
Studying exceptional responders presents many challenges, the first being to define what an exceptional response is and what it is not, explained Ivy. “This definition relies on the existence of data that a particular therapy will produce particular responses in groups of patients with similar tumors, as defined by organ of origin,” she said.
Other challenges include obtaining tumor tissue and all the relevant clinical data, such as the number of prior treatments and the patient’s response, as well as any known molecular characteristics (eg, HER2/NEU amplification, estrogen-receptor expression, germline mutations). “We also do not have data on other exposures, such as smoking or chemical exposure,” she said. “In addition, when patients are not on clinical trial, the data are not uniformly obtained ― such as that scans may not be performed at particular intervals.”
Importantly, the molecular tools used to analyze tumors were not available in the past, so many trials did not collect tumor tissue for subsequent research. “Even now, we are learning that there are characteristics beyond DNA and RNA that are potentially important to the ability of a tumor to respond, such as the immune system or epigenetic changes,” she said.
From August 2014 to July 2017, a total of 520 cases were proposed by clinicians as possibly involving exceptional responders, and 222 cases met the criteria.
Analyzable tissue was available for 117 patients. Most of the responders (n = 80, 68.4%) had been treated with combination chemotherapy regimens; 34 patients (29.0%) had received one or more antiangiogenesis agents. In addition, six patients had an exceptional response following treatment with immune checkpoint inhibitors. The final analysis included 109 cases.
One exceptional responder was a woman with metastatic squamous lung cancer that was treated with paclitaxel and carboplatin. The patient achieved a 41-month complete response (expected rate, <10%). Another patient with esophageal adenocarcinoma who was treated with docetaxel and cisplatin experienced a partial response that lasted 128 months (reported median response duration, 24 months). After the patient’s tumor recurred, he experienced for the second time a response to concurrent chemoradiation with the same drug regimen.
Overall, potentially clinically relevant germline mutations were identified in six tumors. Pathogenic BRCA1 or BRCA2 mutations were found in two breast cancer patients, one patient with non–small cell lung cancer, and one patient with rectal cancer. A breast cancer patient had a pathogenic BRCA1 germline mutation, and another had a likely germline mutation in CHEK2. A patient with poorly differentiated lung cancer and a history of breast cancer had a PALB2 mutation.