Some forms of cancer behave in an unexpected way

Tumor size may not be an accurate method of predicting lymph node involvement and disease progression in some breast cancers, according to investigators at the Research Institute of the McGill University Health Centre (MUHC). Their findings show that some types of breast tumors do not “play by the rules” and possibly, are more dangerous than previously believed.

“We have identified a group of breast cancer tumors that don’t conform to previous observations made in the general population of women with breast cancer,” says MUHC geneticist and lead investigator, Dr. William Foulkes. “For these tumors there is only a very weak correlation between tumor size, the local spread of cancer cells and the likely severity of disease.”

An associate professor in the Departments of Medicine, Human Genetics and Oncology at McGill University, Foulkes and his colleagues studied over 1500 women with breast cancer. Women with breast cancer who also had a mutation in particular gene, BRCA1, had unusual tumors. These tumors did not behave as expected – there was no clear correlation between tumor size and associated cancer in the axillary lymph nodes. This was not true for breast cancers in the general population, or those related to another breast cancer susceptibility gene, known as BRCA2.

These results are surprising, because previous studies have indicated that BRCA1-related breast cancers tend to behave aggressively. Thus, the preferred route of spread of BRCA1-related breast cancers may be different from other types of breast cancer. According to Foulkes, these observations have important implications for early diagnosis and treatment of women who carry this gene.