Background: Ductal carcinoma in situ (DCIS) is a neoplastic proliferation of epithelial cells which is confined within the basement membrane of the mammary ductal-lobular system. It is of interest to determine to what extent the potential to metastasize increases for DCIS patients when the basement membrane is breached (i.e. microinvasion is present).
Methods: We retrieved the records of 525,395 women who had either first primary DCIS or small (≤ 2.0 cm) node-negative invasive breast cancer in the Surveillance, Epidemiology and End Results (SEER) registries database (1990-2013). For each patient, we extracted information on year of diagnosis, age at diagnosis, tumour size, tumour grade, oestrogen receptor status, use of radiotherapy, type of surgery, cause of death and follow-up time. We classified patients into four groups, according to the size of the invasive component of the primary tumour. We estimated the actuarial rate of breast cancer-specific mortality at ten and 20 years for women in each size category.
Results: We identified 161,394 women with pure DCIS, 13,489 women with microinvasive carcinoma (≤ 0.1 cm of invasion), 153,856 women with invasive cancer 0.2-1.0 cm in size and 196,656 women with invasive cancer 1.1-2.0 cm in size. The 20-year actuarial breast cancer-specific mortality rate was 3.8% for women with pure DCIS, was 6.9% for women with microinvasive carcinoma, was 6.8% for women with invasive cancer 0.2-1.0 cm in size and was 12.1% for women with invasive cancer 1.1-2.0 cm in size. The adjusted hazard ratio for death associated with microinvasive carcinoma (vs. pure DCIS) was 2.00 (95% CI 1.76-2.26; p < 0.0001).
Conclusions: In terms of prognosis, microinvasive cancer more closely resembles small invasive cancer 0.2-1.0 cm) than pure DCIS. For invasive cancers under 1.0 cm, size has little impact on mortality.
Keywords: Breast cancer; DCIS; Microinvasion; Survival.