Background: Prognosis of patients with node-negative disease and tumor size <1 cm is a matter of controversy. While data exist to clearly correlate small tumor size to better prognosis, the fact that very small breast cancers may express biological markers of dire prognosis leads many to ignore small tumor size during treatment decision-making.
Patients and methods: Data from 425 patients classified as having node-negative pT1mic, pT1a or pT1b after surgery (from April 1997 to December 2001) at the European Institute of Oncology, were analyzed to be described as disease-free according to prognostic variables including: Ki-67 (<20% versus > or =20% of the cells), ER (absent versus positive > or =1% of the cells), PgR (absent versus positive > or =1% of the cells), grade, overexpression or amplification of HER2/neu, presence of peritumoral vascular invasion and age (by decade). The median follow-up for this cohort of patients was 43 months.
Results: No local or distant relapse was observed for patients with pT1mic breast cancer; 4-year disease-free survival for pT1a and pT1b was 97.0% and 97.6%, respectively. In both univariate and multivariate analyses the most relevant prognostic factor for this low-risk population was Ki-67 labeling. The 4-year disease-free survival was 99.2% for tumors with low Ki-67 and 93.3% for tumors with high Ki-67 (> or =20%) labeling. The hazard ratio (HR) for patients with high Ki-67 was 12.9 (95% CI 1.5-112.0, P=0.02).
Conclusions: Within the first 4 years, microinvasive breast cancer parallels ductal carcinoma in situ (DCIS) rather than invasive carcinoma. Costs and benefits of adjuvant therapy should be accurately weighted in these patients. Patients with pT1a and pT1b, node-negative disease have a limited but substantial risk of recurrence and therefore adjuvant therapy, according to endocrine responsiveness of the tumor and patient preference, should continue to be offered as a reasonable treatment option.