BriaCell Therapeutics’ Phase 1/2a study of the breast cancer vaccine BriaVax is proceeding according to plan, the company recently announced.

Six patients with advanced breast cancer have received the therapeutic vaccine, which intends to trigger an immune response against the cancer. The study (NCT03066947), in which researchers treated and evaluated the first three patients in a sequential manner, so far has not flagged potential safety issues.

The Phase 2a part of the study started when the initial three patients were evaluated, and the company expects to share data on the first 10 patients in early 2018.

“Recruitment continues to proceed as projected, despite the challenges presented in recruiting late-stage cancer patients,” the company wrote in a press release.

BriaVax is made up of injections of cells that have been genetically modified to release GM-CSF — an immune system activator. An earlier small Phase 1 study showed that the treatment triggered rapid and nearly complete eradication of metastatic breast cancer in the breast, lung, soft tissue, and brain.

Patients receiving the cell vaccine are pre-treated with the immunosuppressant cyclophosphamide and get Intron A (interferon alpha-2b) after the vaccine.

In addition to testing BriaVax in patients, the company works on developing a so-called companion diagnostic, called BriaDx, to be used together with the vaccine. The idea is that BriaDx would identify patients most likely to benefit from the treatment.

While researchers are hopeful that BriaVax will trigger robust responses in these women with advanced and metastatic breast cancer, they are open to the possibility that BriaVax alone might not be sufficient.

Patients in the Phase 1/2a trial who progress on BriaVax treatment have the opportunity to instead enroll in a Phase 1/2 trial (NCT03328026) where BriaVax is combined with either Bristol-Myers Squibb’s Yervoy (ipilimumab) or Keytruda (pembrolizumab), a drug produced by Merck (MSD outside the U.S. and Canada).

Both Yervoy and Keytruda are so-called checkpoint inhibitors, releasing the brakes on the immune system enforced by the cancer. Researchers believe that these drugs may boost the anticancer effect of BriaVax.

At the moment, BriaCell is testing the vaccine at three clinical sites in California, Florida, and Washington, which are all recruiting patients. Additional clinics will be included in the coming months, according to BriaCell.

Patients interested in enrolling can get more information, including contact details, at the trial registration website here.