TORONTO - The various subtypes of ovarian cancer are actually distinct diseases, says a new study which argues lumping them together is impeding the search for more effective treatments for this deadly form of cancer.
The study findings won't have an immediate impact on the way women with ovarian cancer are treated, cautioned senior author Dr. David Huntsman. But he said they should trigger changes in the way ovarian cancer research is conducted, potentially accelerating the discovery of more effective treatments.
"We think it's really going to speed things up. It's going to make it much easier to determine success if you're dealing with a pure population of patients where everybody has the same disease," said Huntsman, a researcher with Vancouver General Hospital and the British Columbia Cancer Agency.
He said for several years his research group has believed the habit of treating ovarian cancer subtypes as one disease for research purposes was "the single greatest obstacle towards finding new biomarkers for ovarian carcinoma and also eventually new treatments."
"But it's easy just to say these things. You have to prove it. So this paper provides the evidence to treat them as different diseases," Huntsman said.
Experts who were not involved with the study agreed the findings hold promise for advances in treatment and diagnosis of ovarian cancer.
Dr. Steven Narod, a leading breast and ovarian cancer expert at Women's College Research Institute in Toronto, noted the realization that different types of breast cancer needed to be treated differently led to advances in the care of women with breast cancer.
But Huntsman and others also admitted the findings would substantially complicate efforts to find a blood test that could detect ovarian cancers before they become life threatening.
The study was funded by the Canary Foundation, a non-profit organization that supports research aimed at developing early detection tools for cancer. It was published Tuesday in the Public Library of Science journal PLoS Medicine.
Better detection tools and treatments for ovarian cancer are badly needed. Though ovarian cancer is highly treatable in the early stages, fewer than 20 per cent of cases are found then. And late stage ovarian cancer has a poor prognosis.
Statistics compiled for the Canadian Cancer Society suggest only 40 per cent of women in this country who are diagnosed with ovarian cancer will survive five years after their diagnosis. The society estimates 2,500 cases of ovarian cancer will be diagnosed in Canada this year and 1,700 women will die of the disease.
In this research, Huntsman and colleagues from the two Vancouver institutions along with American and German scientists set out to establish that the subtypes of ovarian cancer are distinct diseases by studying the proteins or biomarkers created by the cells in different tumour types.
They studied tissue from 500 tumours collected from 1984 to 2000, checking them for the presence of 21 different biomarkers that have been found in ovarian cancers.
They found significant differences in the pattern of biomarkers present in five types of ovarian cancers - low and high grade serous, clear cell, endometrioid and mucinous. But they found consistency within the types, meaning that a protein evident in an early stage clear cell cancer was also present in late stage clear cell tumours.
The analysis showed that lumping the types together could muddy findings. For instance, when the tumours were studied en masse, the presence of the protein WT1 seemed to predict a woman's chances of survival were poor. But when the high grade serous tumours were studied on their own, the presence of WT1 turned out to be a positive sign.
Several experts said cancer pathologists have known for some time that ovarian cancers are sufficiently different that they need to be studied type by type. But the claim has been met with skepticism on the part of some clinicians.
"Even though we've been telling medical oncologists for years their chemotherapy doesn't work there (in clear cell cancers) they've really rejected the notion of doing subtype analyses," said Dr. Patricia Shaw, a pathologist at Toronto's Princess Margaret Hospital and director of that hospital's biobank, the country's largest ovarian tissue bank and database.
"So that means those patients haven't really had any efforts put forth to finding treatments that are going to help their disease."
Barbara Vanderhyden, who holds a chair in ovarian cancer research at the University of Ottawa, said success is more likely if researchers follow the advice contained in the study.
"The bottom line is we're barking up the wrong tree if we think that we can treat all ovarian cancer patients the same way," said Vanderhyden, who is also a senior scientist at the Ottawa Health Research Institute.
"And that by looking at them as subgroups, as subtypes, we're more likely to find something in common within a subtype that will alter how we treat those patients."
