Evaluation of prognostic factors in lymph node negative (LNneg) invasive lobular cancers (ILCs). Prospective analysis of proliferation and other prognosticators in 121 LNneg ILCs (119 months median follow-up, range 19-181), without adjuvant chemotherapy. ILC subtype was assessed in accordance with WHO-2003 criteria. Immunohistochemical E-cadherin and estrogen receptor were used. With a median follow up time of 83 months (range 19-181), 30 of the 121 (25%) ILC patients developed distant metastases and 27 (22%) died. None of the cases classified as solid/pleomorphic lobular were E-cadherin or estrogen receptor positive, contrasting the other ILCs. The solid/alveolar ILCs (n = 17) had a worse survival (50%) than the other ILCs (n = 104; 83%, P < 0.0001). Mitotic activity index (MAI) (but not nuclear grade or tubule formation) was prognostic with a threshold 0-5 versus >5 (=MAI-5) (contrasting MAI < 10 vs. > or = 10 in breast cancers in general; 85 and 54% survival, P < 0.0001). In multivariate analysis only subtype and MAI but none of the other characteristics had independent prognostic value. Histologic subtype and MAI have independent prognostic value in node negative invasive lobular cancers.