A non-Hodgkin lymphoma that arises from the breast. There is no history of extramammary breast non-Hodgkin lymphoma and ipsilateral axillary lymph node involvement does not exclude the diagnosis of primary breast non-Hodgkin lymphoma. Most patients present with a painless breast lump. The vast majority of cases are B-cell non-Hodgkin lymphomas. Diffuse large B-cell lymphoma, follicular lymphoma, and extranodal marginal zone B-cell lymphoma of mucosa associated lymphoid tissue are the most common types of primary non-Hodgkin lymphoma of the breast. [from
NCI]