AMSTERDAM – An experimental combination of PET scanning and a positron-emitting form of erlotinib appeared to work as a noninvasive way of identifying patients with advanced non–small cell lung cancer tumors that have the right genotype to receive erlotinib therapy.
"[11C]erlotinib PET shows promise as a noninvasive, in vivo means of selecting patients who may benefit from thymidine kinase inhibitor therapy," Dr. Idris Bahce said, reporting on a pilot study of 10 patients. Erlotinib (Tarceva) is from the thymidine kinase inhibitor drug class.
Dr. Idris Bahce
In his study, uptake of 11C-labeled erlotinib was significantly linked to the patients’ having an activating mutation in their epidermal growth factor receptor (EGFR) gene, specifically an exon 19 deletion.
Patients positive for erlotinib uptake on the PET scan also showed a tendency for better clinical responses to a therapeutic erlotinib regimen, reported Dr. Bahce, a pulmonologist at VU University, Amsterdam, during the World Conference on Lung Cancer.
Until now, the only way to identify advanced non–small cell lung cancer (NSCLC) tumors that are candidates for treatment with a tyrosine kinase inhibitor has been to biopsy the tumor and run an in vitro genetic analysis on the tumor cells. That can be challenging in some patients, such as when the tumor is not easy to biopsy, a limited amount of tissue is available, or the tumor is genetically heterogeneous. To get a reliable result from biopsy and testing, at least 30% of the specimen must contain malignant cells, Dr. Bahce said at the conference, sponsored by the International Association for the Study of Lung Cancer.
"It is a very early study, but ... it’s important because personalized treatment [for cancer] has gone to the next level, where we use new agents and match them to the right patients by doing biopsies," commented Dr. Roy S. Herbst, chief of medical oncology at the Yale Cancer Center in New Haven. "The PET method also allows physicians to assess the volume of cancer carrying the EGFR mutation following treatment, a way to track treatment efficacy," said Dr. Herbst in an interview.
"Instead of getting tissue at one point in time, you can image more frequently. It’s a way to track the course of treatment noninvasively," and in real time, he said.
He also predicted that the [11C]erlotinib PET test will become commercialized, although currently Dr. Bahce’s studies do not have any commercial funding.
"This is a proof of concept study," commented Dr. Luis Paz-Ares, chief of medical oncology at University Hospital Virgin del Rocio in Seville, Spain. "We need to define the positive predictive value and the negative predictive value" of the test, he added. The long-term future of a test like this may also be limited because future testing will probably need to look at multiple biomarkers, Dr. Paz-Ares said.
The study enrolled five patients with advanced NSCLC who had exon 19 deletion EGFR mutations, and five advanced NSCLC patients with wild-type EGFR genes. Each patient underwent a pair of [11C]erlotinib PET scans, each preceded by a [15O]water PET scan to assess blood perfusion of the tumors. A 4-hour interval separated the two sets of scans.
The scan results showed that the volume of distribution of the tagged erlotinib in the patients with EGFR mutations ran about 50% higher than in the patients with wild-type tumors, a difference that was significant (P = .03).
Clinically, two of the five wild-type patients had nonetheless received erlotinib treatment prior to testing, and neither patient responded, with both showing progressive disease.
Three of the five patients with an EGFR mutation began receiving erlotinib treatment after testing and responded. In one of these patients, the tumor remained in check for 13 months. In a second patient, the tumor began to progress after 17 months of no progression on treatment. In the third patient, the tumor began to progress again after about 4 weeks of no progression on erlotinib treatment, Dr. Bahce said. A fourth patient went on erlotinib treatment before testing, and did not respond and continued to have progressive disease.
The two patient subgroups showed no difference in blood perfusion into the tumors, or in EGFR expression in cell membranes.
Dr. Bahce said he had no disclosures.