Patients will first undergo screening and mandatory collection of core tumor biopsies for study analysis. Patients are randomized (1:1:1) to receive Letrozole 2.5mg daily, oral Vinorelbine 50mg 3 days a week or Letrozole 2.5mg daily and oral Vinorelbine 50mg 3 times a week. After 3 weeks of treatment, patients will undergo surgery, and both pre-treatment and post-treatment surgery samples will be analyzed. Alternatively, if surgery will be delayed, a tumor core biopsy will be collected. Anyway, post-treatment sample should be collected within 5 days after end of treatment in order to observe the biological response.