There are four distinct types of breast cancer, study finds

Research supports theory that cancers should be treated based on genetic origin

Hundreds of researchers have identified four different categories of breast cancer using genome sequencing, a finding that is expected to provide a "road map" for treatment., the New York Times reports.

The study—published in the journal Nature—is part the Cancer Genome Atlas project, a federal initiative that aims to analyze the genetics of 20 different types of cancer.

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Study details

In the first comprehensive genetic analysis of breast cancer, nearly 350 researchers sequenced the genomes of 825 tumors. They focused on early breast cancers that had not spread to other parts of the body in an effort to identify and attack genetic changes in the disease before it metastasized.

Based on their analysis, the researchers identified four different types of breast cancer:

  • Luminal A: A less aggressive, estrogen-positive cancer;
  • Luminal B: A more aggressive, estrogen-positive cancer;
  • HER2-enriched: Includes many, but not all, HER2-positive breast tumors or tumors that express significant quantities of the HER2 protein; and
  • Basal-like: Includes many, but not all, triple-negative breast cancers. This variant resembles cells found in skin and sweat glands, and is more similar to ovarian cancer than other breast cancers types.

Scientists had previously categorized breast cancer into three different types. "We have been lumping things together that shouldn't be lumped together," notes Christopher Benz, a University of California-San Francisco oncologist who helped lead the study.

According to the Times, scientists were surprised to learn that basal-like, triple-negative breast cancers more closely resembled ovarian cancer and a certain type of lung cancer.

The finding suggests that ovarian cancer treatments may help fight this breast cancer variant. It also provides credence to the growing medical view that cancers should be categorized by their genetic origin rather than where they grow in the body.

Findings expected to launch wave of new trials, treatments

The study found that unique sets of genetic changes may be causing individual tumors to grow within the four major groups of breast cancer. This finding is expected to inspire new ideas for precise treatments designed to inhibit these genetic aberrations, the Times reports.

Scientists already have discovered 40 genetic mutations that new drugs may be able target, some of which are already being developed for other types of cancer that have similar mutations (Kolata, New York Times, 9/23; Flinn, Bloomberg Businessweek, 9/24; Colliver, San Francisco Chronicle, 9/23).

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