According to a research conducted by the Ottawa Hospital, a common treatment for erectile dysfunction combined with the flu vaccine may be able to help the immune system mop up cancer cells left behind after surgery.

The study showed that this unconventional strategy can reduce the spread of cancer by more than 90 percent in a mouse model. It is now being evaluated in a world-first clinical trial. "Surgery is very effective in removing solid tumours," said senior author Rebecca Auer. "However, we're now realizing that, tragically, surgery can also suppress the immune system in a way that makes it easier for any remaining cancer cells to persist and spread to other organs. Our research suggests that combining erectile dysfunction drugs with the flu vaccine may be able to block this phenomenon and help prevent cancer from coming back after surgery."

The current study investigated sildenafil (Viagra), tadalafil (Cialis) and an inactivated influenza vaccine (Agriflu) in a mouse model that mimics the spread of cancer (metastasis) after surgery. Auer is now leading the first clinical trial in the world of an erectile dysfunction drug (tadalafil) and the flu vaccine in people with cancer. It will involve 24 patients at The Ottawa Hospital undergoing abdominal cancer surgery. This trial is designed to evaluate the safety and look for changes in the immune system. If successful, larger trials could look at possible benefits to patients.

"We're really excited about this research because it suggests that two safe and relatively inexpensive therapies may be able to solve a big problem in cancer," said Auer. "If confirmed in clinical trials, this could become the first therapy to address the immune problems caused by cancer surgery." Using a variety of mouse and human models, Auer's team also made progress in understanding how erectile dysfunction drugs and the flu vaccine affect cancer after surgery.

Normally, immune cells called natural killer (NK) cells play a major role in killing metastatic cancer cells. But surgery causes another kind of immune cell, called a myeloid-derived suppressor cell (MDSC), to block the NK cells. Auer's team has found that erectile dysfunction drugs block these MDSCs, which allows the NK cells to do their job, fighting cancer. The flu vaccine further stimulated the NK cells.

"Cancer immunotherapy is a huge area of research right now, but we're still learning how best to use it in the time around surgery," said first author Lee-Hwa Tai. "This research is an important step forward that opens up many possibilities." The study is published in the journal OncoImmunology.