A type of breast cancer has been found to have genetic similarities to ovarian cancer tumours.

This week's online issue of the journal Nature maps gene mutations of breast cancer tumours.

Researchers confirmed the existence of four main subtypes of breast cancer. (Enrique Castro-Mendivil/Reuters)

"For basal-like breast tumours, it's clear they are genetically more similar to ovarian tumours than to other breast cancers," study co-author Dr. Matthew Ellis, chair of medical oncology at Washington University School of Medicine in St. Louis.

"Whether they can be treated the same way is an intriguing possibility that needs to be explored," he added in a release.

Basal-like breast cancer tumours are aggressive and account for about 10 per cent of breast cancers. There are chemotherapies to treat the similar form of ovarian cancer, which also tends to be aggressive, said John Bartlett, director of transformative pathology at the Ontario Institute for Cancer Research in Toronto.

In the study, researchers, including a team from the BC Cancer Agency, analyzed genetic samples from tumours taken from 825 women with breast cancer using six different technologies.

Mutation road map

They were looking for defects in the DNA, RNA and proteins in the tumours to form a detailed classification.

The findings are important for cancer researchers, who hope to use the data to focus their investigation on fewer mutations for each subtype, Bartlett said.

"We know the key features in the landscape of the disease now but we don't know what their impact is in terms of if you have that mutation," Bartlett said of the potential benefits to patients. "That is the next phase of research. It's like having a map of Canada. You know where the place names are but you don't know the best place to visit yet."

To find the best places will take more research linking genetic changes to patient experiences. Investigators need to test whether treatments work and survival improves.

The researchers confirmed four main subtypes of breast cancer:

• Luminal A, which tend to be less aggressive.
• Luminal B, which tend to be more aggressive.
• Basal-like tumours, often aggressive tumours that are also known as triple-negative. These tumours lack receptors for the hormones estrogen, progesterone or human epidermal growth factor 2 (HER2) and do not respond to hormonal treatments.
• HER2-positive breast cancer, which refers to the over-expression of the gene HER2, a type of protein, that is targeted by the drug Herceptin.

The latest findings add more evidence that cancer is actually many different diseases, said Professor David Bowtell, director of genomics and genetics at Melbourne's Peter MacCallum Cancer Centre.

"There's a sort of fragmentation that's occurring," he told the Australian Broadcasting Corporation.

"What we're also finding, though, is that there are unexpected parallels between cancers that are from quite different parts of the body."

It is hoped that the findings will help researchers over the next 10 years to discover new targets and pathways in individuals, said breast cancer specialist Dr. Daniel Rayson of Halifax's Capitol Health.

For those who treat cancer patients, learning more creates a barrier to recruiting patients for clinical trials. The pool of people who are eligible to participate in the research shrinks as more breast cancer subtypes are discovered, Rayson noted.

"As we learn more it gets harder to do the relevant clinical trials and without clinical trials new treatments don't come to the population," he said.

The report is the latest from the Cancer Genome Atlas, an international project investigating genes that contribute to brain, colorectal, lung, and ovarian cancers.

With files from CBC's Amina Zafar, Pauline Dakin and the Australian Broadcasting Corporation