Background: The 2011 St Gallen guidelines recommend the use of Ki67 as a surrogate marker for luminal A and Luminal B breast cancer subtypes. Pts with luminal B subtypes should be considered for adjuvant chemotherapy. The guidelines also recognize the Oncotype DX RS as a predictor of chemotherapy benefit. The aim of this study is to assess the distribution of the RS in luminal A and luminal B breast cancer subtypes as defined by Ki67. Methods: Data from 91 pts with invasive breast cancer for which Oncotype DX results and pathology data were available. Pathological assessment was evaluated by the same pathologist. Estrogen (ER) and progesterone (PR) receptor was assessed by immunostaining (cut-off 10% nuclear staining). Ki67 was assessed by IHC [high (≥14%) and low (< 14%)]. Grading was performed by using Nottingham grading system. Results: Median age: 50 years (range: 35-78); premenopausal status: 49 pts (53.8%). Median tumor size: 1.5 cm (0, 3-6); Median of Ki 67 index: 15. 5 (range: 3-63); Median ER: 93 (35-100) and PR: 85(0-100). Sixty nine pts (75.8%) had negative-lymph nodes. RS was low in 56 (61. 5%) cases, intermediate in 24 (26. 4%), and high in 11 (12. 1%). The median RS was 16 (range 3-55). Forty six (51%) tumors were classified as luminal B (according to high Ki 67) and 38 (41.7%) as Luminal A. In the Luminal B group RS was low in 28 (61%) pts, intermediate in 10 (22%) and high in 8 (17%) while in the Luminal A group 23 (61%) had low RS; 13 (34%) intermediate and 2 (5%) high RS. RS changed the first treatment recommendation in 23 (50%) cases of Luminal B subtype vs. 10 (26%) cases in Luminal A subtype (p=0.013). Conclusions: Although based in a small case series, the results show that a substantial number (61%) pts with Luminal B breast cancer subtype had a low RS, therefore preserving them from adjuvant chemotherapy treatment. In addition, 5% of patients with Luminal A breast cancer had a high RS and thereby likely to benefit from chemotherapy. The wide range of RS in both Luminal B and Luminal A breast cancer subtypes confirm the important role of Oncotype DX in treatment decision- making.