OncoSec Medical Inc. said a mid-stage study of its drug Tavo combined with Merck & Co. Inc.'s Keytruda showed longer response duration and the absence of detectable disease in skin cancer patients.

Updated results from the phase 2b study, dubbed Keynote-695, showed one of the previously assessed partial responses has now become a complete response — the best treatment result for cancer — at six months. In November, OncoSec reported two of nine patients with advanced melanoma that could not be surgically removed had a partial response, or a decrease in their cancer, following 12 weeks of treatment. One patient had stable disease, signifying the melanoma was neither growing nor shrinking.

"Complete responses in this patient population are rare," OncoSec President and CEO Daniel O'Connor said. "Durable responses reaching the six-month mark demonstrate that the benefits of Tavo are clinically meaningful."

Additionally, the clinical trial showed advanced melanoma patients responded to the combination therapy for six months.

"The tumor responses seen in this trial, now independently verified by a blinded review at the first assessment, deepening and continuing for months, gives us confidence in the potential of this treatment combination for patients who are non-responsive to anti-PD-1 therapy," said Adil Daud, lead principal investigator of the study.

Eligible patients in the clinical trial had resistant, locally advanced disease or disease that has spread to new areas of the body. The stage 3/4 metastatic melanoma in these patients had definitively progressed on a full-course of anti-PD-1 treatment with blockbuster drugs Keytruda, also known as pembrolizumab, or Bristol-Myers Squibb Co.'s Opdivo, also called nivolumab.

"It is becoming clear that Tavo can reverse PD-1 resistance in refractory metastatic melanoma patients. This is important because the majority of melanoma patients do not respond to PD-1 treatment," Daud added.

Based on the most recent study results, OncoSec intends to file for accelerated approval for the Tavo-Keytruda regimen by the end of 2019 or early 2020.

The U.S. Food and Drug Administration had granted both orphan-drug and fast-track designations to Tavo.