Potential New Therapy for Breast Cancer

At the Univeristy of Guelph and McMasters University in Canada, thirty cats over the next two years will be treated with virus immunotherapy in addition to receiving surgery for their breast cancer.

As in humans, breast cancer occurs in felines, and it is usually a particularly aggressive cancer.  An additional hazard in cats is that it is typically not discovered until it has already spread to other parts of the body, particularly to the bone.  The current standard treatment for cats is surgery, as their breast cancer responds poorly to chemotherapy.  Even with removal of the tumor, it most often relapses within 6-8 months.

A cell showing two plaques caused by infection with an oncolytic virus.
Author: Viraltonic,  under the Creative Commons Attribution-Share Alike 3.0 Unported license.

The cats undergoing this trial will receive an injection of an oncolytic virus, which is a virus that specifically attacks cancer cells.  Most often, these viruses are genetically engineered, however there are some that occur naturally.  Two examples of naturally occurring oncolytic viruses are the SVV-001, and the reovirus.  More naturally occurring viruses are now being tested for potential oncolytic properties.  The feline patients will receive one injection prior to the surgery, and a second one a month after the surgery is completed.  If the results are positive, they intend to move this to human trials.

Oncolytic viruses destroy cancer cells via a process called lysis.  This process involves the killing of a cell by compromising its wall or membrane.  When these cancer cells are ruptured and killed, they release the newly made infectious material to target other cells in the tumor.  So the benefit is two pronged.  The virus will both directly kill cancer cells, while also triggering a boosted immune response from the patient.

The vaccine given to the cats prior to the surgery will attempt to do the latter; it is a non-replicaing adenovirus.  The second one given a month later will be a Maraba virus.  This second one will not be a simple injection, but an infusion into the bloodstream to target cells wherever they may be remaining in the body.  This virus has been engineered to only have the capacity to replicate in cancer cells.  This property renders the virus harmless to the patient.

It should be noted that oncolytic viruses have been tried in other cancers, one in particular, named talimogene laherparepvec, has been proven effective in advanced clinical trials for the deadly skin cancer melanoma.  Currently in Phase III, it stands a remarkable chance to be the first oncolytic virus approved for cancer treatment.