Triple negative breast cancer: clinical characteristics in the different histological subtypes.

Purpose: To investigate the clinical behavior of triple negative breast cancer (TNC), including age distribution, occurrence of LN (lymph node) invasion and prognosis in different histological subtypes.

Methods: For this cohort study we used data on 476 patients with newly diagnosed TNC at the University Hospitals Leuven (Belgium) between 1999 and 2009. Of these, 395 received upfront surgery, 68 neoadjuvant chemotherapy and 21 had metastases at diagnosis.

Results: Apocrine and invasive lobular TNC occur more often in older patients compared to IDC-NOS. Of the primarily operated patients with TNC, 35.1% has pathological LN involvement. There were no significant differences in nodal invasion between different histological subtypes, but most subtypes contained few patients. In contrast to previous reports, 6/14 of apocrine TNC had LN involvement. Disease free survival (DFS) was different in different histological subtypes, but group sizes were insufficient to be able to draw firm conclusions. Within the histologically 'homogeneous' IDC-NOS group with primary surgery and outcome data (n = 300), DFS with 3.5 year median follow-up decreased with increasing age, but chemotherapy and radiotherapy were much less frequently given with increasing age. In multivariable analysis, lower age, presence of LN involvement, lack of administration of chemotherapy and radiotherapy were significant predictors of relapse.

Conclusion: TNC is not a uniform disease. Different histological subtypes have different age distribution and behavior. The prognosis of the most common histological subgroup, IDC-NOS, is better in older patients, but this is counterbalanced by significantly decreased use of chemotherapy and radiotherapy.