Survival from contralateral breast cancer

First primary, or unilateral, breast cancer (UBC) cases diagnosed in 1960-89 at the Cancer Institute (WIA), Chennai, India were followed-up until December 31, 1994. Patients with UBC (n = 3163) and those who developed second cancer in the contralateral breast (CBC) after the initial breast cancer (n = 67 or 2.1% of UBC) were analysed. Compared to UBC patients, those who developed CBC were younger at the time of diagnosis of initial breast cancer and had higher frequency of breast cancer among the family members. The relative survival rate takes into account competing causes of death and was estimated as the ratio of observed survival rate to the expected survival rate. The cumulative relative survival from UBC at 5 and 10 years were 51% and 41%, respectively, and the corresponding rates for CBC were 47% and 30%; the survival difference seen between UBC and CBC patients was not statistically significant. The survival rates among younger, middle-aged and older women were significantly different from each other in UBC but not in CBC patients. Both UBC and CBC with early stage disease had a better survival compared to late stage disease. Survival advantage was also seen among both UBC and CBC patients with family history of breast cancer compared to those without. The multivariate analysis by the life table proportional hazards model showed that the age at diagnosis is an independent prognostic factor for breast cancer. The study results should be interpreted in the light of small sample size of second cancers.