Ontario's chief medical officer of health has resigned to focus on her personal battle with cancer.

Sheela Basrur says she has a rare form of cancer — a tumour that affects blood vessels and soft tissue. Known as hemangiopericytoma, it comprises only one per cent of all cancers.

Ontario's Chief Medical Officer of Health Sheela Basrur
(File photo)

"Unfortunately this disease has already spread to other sites and will require many months of further investigation and treatment," she wrote in her resignation letter to Health Minister George Smitherman.

Basrur has been off work for several weeks following emergency back surgery related to the tumour.

"I have never ceased to be amazed by the importance of the issues in my portfolio to the health and well-being of Ontarians," she wrote in the letter.

Basrur was nearly halfway into her five-year term.

Smitherman thanked Basrur for her service in a press release, saying she "led the way to rebuilding public health in this province."

He said Basrur proposed the province's first arm's-length agency for health protection and led the development of the smoke-free Ontario strategy.

Description of hemangiopericytoma:

Hemangiopericytoma is a rare tumour affecting blood vessels and soft tissues. It is one of about a dozen kinds of soft tissue sarcoma. Soft tissue sarcomas can develop in any part of the body, but are most commonly found in the trunk, arms and legs in young patients. Soft tissues, which connect and surround other body parts and organs, include muscles, fat, blood vessels and nerves. A sarcoma refers to a cancerous growth of the soft tissues, usually appearing at first as painless swelling.

"Ontario has one of the most comprehensive tobacco control strategies in North America thanks to Dr. Basrur," said Minister of Health Promotion Jim Watson.

Before her time with the provincial government, Basrur served as the City of Toronto's medical officer of health, where she is best known for dealing with the SARS crisis. 

Dr. George Pasut has been appointed acting chief medical officer of health until a permanent replacement is found.