Time-dependent risk of developing distant metastasis in breast cancer patients according to treatment, age and tumour characteristics

Background: Metastatic breast cancer is a severe condition without curative treatment. How relative and absolute risk of distant metastasis varies over time since diagnosis, as a function of treatment, age and tumour characteristics, has not been studied in detail. Methods: A total of 9514 women under the age of 75 when diagnosed with breast cancer in Stockholm and Gotland regions during 1990-2006 were followed up for metastasis (mean follow-up = 5.7 years). Time-dependent development of distant metastasis was analysed using flexible parametric survival models and presented as hazard ratio (HR) and cumulative risk. Results: A total of 995 (10.4%) patients developed distant metastasis; the most common sites were skeleton (32.5%) and multiple sites (28.3%). Women younger than 50 years at diagnosis, with lymph node-positive, oestrogen receptor (ER)-negative, >20 mm tumours and treated only locally, had the highest risk of distant metastasis (0-5 years' cumulative risk = 0.55; 95% confidence interval (CI): 0.47-0.64). Women older than 50 years at diagnosis, with ER-positive, lymph node-negative and <= 20-mm tumours, had the same and lowest cumulative risk of developing metastasis 0-5 and 5-10 years (cumulative risk = 0.03; 95% CI: 0.02-0.04). In the period of 5-10 years after diagnosis, women with ER-positive, lymph node-positive and >20-mm tumours were at highest risk of distant recurrence. Women with ER-negative tumours showed a decline in risk during this period. Conclusion: Our data show no support for discontinuation at 5 years of clinical follow-up in breast cancer patients and suggest further investigation on differential clinical follow-up for different subgroups of patients.