Women suffering a kind of breast cancer called "triple-negative" are more likely than other breast cancer patients to experience a relapse, a new study by Canadian researchers finds.

Triple-negative breast cancers are estrogen receptor-negative, progesterone receptor-negative, and HER2-negative. The form accounts for about 15 per cent of all breast cancers.

The study, published in the journal Clinical Cancer Research, looked at 1,601 patients diagnosed with invasive breast cancer from 1987 to 1997. Of those patients, 180 were identified as having triple-negative breast cancer.

The researchers found that women with triple-negative breast cancer were almost twice as likely to  relapse. The pattern of relapse had a rapidly rising rate in the first two years after diagnosis, a peak at two to three years, followed by a decline over the next five.

Despite having a high risk of early recurrence, most triple-negative breast cancer patients who had no evidence of progression after eight years, did not recur thereafter. Triple-negative breast cancer patients who remain disease-free for eight years are unlikely to die of breast cancer and can be considered "cured" of their disease.

But if triple-negative breast cancer patients did experience a relapse, the median survival time from relapse to death was nine months, compared to 20 months for other types of breast cancer, the study found.

"Confirming both the aggressive nature of triple-negative breast cancers regardless of other tumour features, and the distinct pattern of relapse will help identify those patients who need aggressive treatment upfront", says Dr. Rebecca Dent, medical oncologist at Sunnybrook Health Sciences Centre and Women's College Hospital, one of the authors of the study.

The study also found that among triple-negative breast cancers, tumours were larger and of higher grade -- meaning they had more cancerous cells within them and were therefore more aggressive in growth. The researchers found that 66 per cent of triple-negative breast cancers have high grade tumours, compared to 28 per cent in other breast cancers.

Mean tumour size was also larger in triple negative breast cancer patients. Only 36 per cent of triple-negative tumours were less than two centimetres, compared to 63 per cent of other breast cancers.