National Breast Cancer Audit data shows that an average of 2.3% of women with invasive breast cancer in one breast also had cancer in the second breast diagnosed either at the same time, or within three months of the first diagnosis. This is called synchronous bilateral breast cancer (SBBC).

The likelihood of SBBC increased with age, ranging from 1.4% in women under 40 to 4.1% in those over 80. It was also slightly more likely among patients with:

  • tumours originating somewhere other than the milk duct (e.g. lobular cancer)
  • large tumours
  • less aggressive forms of cancer (low grade tumours)
  • no cancer in the blood or lymphatic vessels.

Five-year survival for patients with SBBC was not significantly different from patients with cancer in one breast only. For this reason, SBBC is not considered useful in predicting survival for the majority of patients.