Multi-analyte test successfully identifies esophageal cancer patients who are extremely resistant to standard treatment of chemoradiation therapy

Castle Biosciences Inc. has announced that results from a second validation study of its proprietary multi-analyte test, DecisionDx-EC, confirmed the test's ability to identify which esophageal cancer patients are unlikely to benefit from the standard pre-surgical treatment of chemoradiation. The results were reviewed in an oral presentation at the 11th Annual Meeting of the International Society of Gastrointestinal Oncology in Arlington, Virginia. The results suggest that up to 30% of esophageal cancer patients may not benefit from the highly toxic, pre-surgical chemoradiation therapy (CTRT), and instead could have the option of moving directly to surgery and to other treatment options.

Esophageal Cancer Study Results

The DecisionDx-EC test analyzes the localization of three protein biomarkers, NF-kB, Gli1, and SHH, to classify tumors as either responsive to (non-exCTRT) or resistant to CTRT (exCTRT). Testing was performed on formalin-fixed paraffin-embedded esophageal cancer tissue.

In this second, multi-center validation study involving 64 patient cases, 67% of whom had been treated with a regimen that included 5-fluorouracil (5FU), researchers reported a 95% specificity, with positive (PPV) and negative (NPV) predictive values of 88% and 83%, respectively.

These results confirm a similar analysis of an earlier validation study involving 167 patient cases, all of whom underwent a chemoradiation regimen involving 5FU plus platinum/taxanes. This study showed a specificity of 90% and positive (PPV) and negative (NPV) predictive values of 64% and 98%, respectively.

"The standard of care for esophageal cancer, which includes pre-surgical chemoradiation to reduce tumor bulk prior to surgical resection, is not effective for up to 30 percent of patients," said Dr. Sunil Badve, M.D., FRCPath, Professor of Pathology and Laboratory Medicine at the Indiana University School of Medicine. "The ability to identify those patients least likely to benefit from the therapy is an important advancement in managing a patient's disease, allowing them to avoid the toxicities and the delay of surgery and more effective approaches."

GEP Test Results

The Company also presented data from a parallel study of a gene expression profile (GEP) test in development for esophageal cancer. The study assessed the ability of two preliminary gene signatures to predict responsiveness to chemoradiation therapy in tumor samples from 16 patients. The results from this initial study showed that the GEP test predicted treatment response with high accuracy and specificity of 100% and 100%, respectively. The Company plans to further evaluate the GEP test in esophageal and rectal cancer.