BACKGROUND: Mammographic screening and increased awareness has led to an 
increase in the detection of T1 breast tumors that are generally estimated as 
having low risk of recurrence after locoregional treatment. However, even small 
tumors can metastasize, which leaves us with the question for the necessity of 
adjuvant treatment. Therefore, additional prognostic markers are needed to 
tailor adjuvant systemic treatment for these relatively low-risk patients. The 
aim of our study was to evaluate the accuracy of the 70-gene MammaPrint 
signature in T1 breast cancer.
MATERIALS AND METHODS: We selected 964 patients from previously reported studies 
with pT1 tumors (<or=2 cm). Frozen tumor samples were hybridized on the 70-gene 
signature array at the time of the initial study and classified as having good 
prognosis or poor prognosis.
RESULTS: The median follow-up was 7.1 years (range 0.2-25.2). The 10-year 
distant metastasis-free (DMFS) and breast cancer specific survival (BCSS) 
probabilities were 87% (SE 2%) and 91% (SE 2%), respectively, for the good 
prognosis-signature group (n = 525), and 72% (SE 3%) and 72% (SE 3%), 
respectively, for the poor prognosis-signature group (n = 439). The signature 
was an independent prognostic factor for BCSS at 10 years (multivariate hazard 
ratio [HR] 3.25 [95% confidence interval, CI, 1.92-5.51; P < .001]). Moreover, 
the 70-gene MammaPrint signature predicted DMFS at 10 years for 139 patients 
with pT1ab cancers (HR 3.45 [95% CI 1.04-11.50, P = .04]).
CONCLUSIONS: The 70-gene MammaPrint signature is an independent prognostic 
factor in patients with pT1 tumors and can help to individualize adjuvant 
treatment recommendation in this increasing breast cancer population.