Left laterality is an independent prognostic factor for metastasis in N3 stage breast cancer.

Purpose: Development of metastasis in patients with breast cancer (BC) is the most important negative prognostic factor and this process mainly begins with lymphatic involvement. Therefore, axillary, subclavicular, internal mammary or supraclavicular nodal involvement is a crucial step before metastasis. Anatomical differences between the right and left lymphatic drainages of the breasts may significantly affect the rate, site and time to development of distant metastasis.