Dr. Sheela Basrur, Ontario's chief medical officer of health, is resigning after being diagnosed with a rare form of cancer.

In a letter to Health Minister George Smitherman, Basrur says back problems she had been suffering were caused by a rare type of vascular tumour known as a hemangiopericytoma.

She says the disease has already spread and will require many months of further testing and treatment.

Basrur has been the province's chief medical officer since 2004 and was front and centre during the province's SARS outbreak three years ago as Toronto's chief medical officer of health.

She developed a national profile during her work on the outbreak.

Smitherman praised Basrur for her work during her term.

"Dr. Basrur has led the way to rebuilding public health in this province," he said in a statement Wednesday.

"Dr. Basrur is a dedicated professional, an excellent communicator and a great leader who is truly passionate about making this province and its people as healthy as possible."

Basrur said her decision to step down was "extremely difficult ... both professionally and personally."'

"The dual roles of chief medical officer of health and ADM (assistant deputy minister of public health) have heavy responsibilities that cannot be done by half-measures," she said.

"They demand a more than full-time commitment of energy and dedication to work, carried out under complex and challenging conditions, including but not limited to leadership in times of public health crisis and emergencies."

Basrur's list of accomplishments with the province includes:

• Leading the development of the Smoke-Free Ontario Strategy;
• Launching a review of all programs and services delivered by Ontario's 36 health units; and
• Proposing Ontario's first arms-length agency for health protection.

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

"Thanks to her energy, her dedication and leadership we have made great progress in tackling tobacco use, the No. 1 cause of preventable disease and death in this province."

Her work for the City of Toronto included establishing DineSafe, a program that gives the public access to restaurant inspection information. The initiative set the standard for transparency for many of the province's health units.

The government announced Dr. George Pasut as the acting chief medical officer of health as a search for a permanent replacement is underway.

Dr. Pasut currently works with the Ministry of Health and Long-Term Care and was the medical officer of health in Simcoe County for nine years, which followed a seven-year stint with the health ministry.

"Dr. Pasut has solid leadership skills and strong working relationships with the public health community," Smitherman said.

With files from The Canadian Press