Prognosis of metachronous contralateral breast cancer: importance of stage, age and interval time between the two diagnoses.

Studies comparing the prognosis after contralateral breast cancer (CBC) with that after unilateral breast cancer (UBC) shows conflicting results. We assessed the risk of breast cancer-specific death for women with metachronous CBC compared to those with a UBC in 8,478 women with invasive primary breast cancer registered in the Guy's and St. Thomas' Breast Cancer Tissue and Data Bank. Risk factors associated with breast cancer-specific death for women with CBC were estimated using Cox proportional hazards modelling. Prognoses after UBC and CBC were compared, with survival time for women with CBC calculated: (i) from CBC, (ii) from the initial cancer with CBC as a time-dependent covariate. Women diagnosed with CBC within 5 years after the initial primary breast cancer had a worse prognosis than those with CBC after 5 years and those with UBC. Women with CBC who had positive lymph nodes at the initial breast cancer diagnosis were at an increased risk of dying from breast cancer compared to those without [HR 2.5 (95% CI 1.5-4.0)]. For all stages of the initial breast cancer, a worse prognosis was observed after CBC. CBC increased the hazard originating from the initial cancer at any follow-up time, but the highest hazards were associated with a short interval to CBC. Metachronous CBC adds to the risk of dying from breast cancer. The risk increases substantially when it occurs shortly after the initial cancer, indicating a CBC in some instances may be an indicator of active distant disease. The occurrence of CBC implies a new surveillance and therapeutic situation.