There are many causes of swollen lymph nodes under the armpit, such as lymphadenitis and hematologic diseases such as malignant lymphoma, which do not cause breast swelling and pain. However, in the case of enlarged lymph nodes in the armpits caused by breast cancer and other diseases, it may be accompanied by breast swelling and pain. 1. Lymphadenitis: It is more common due to bacterial infection, in which the lymph nodes under the armpit can be enlarged and painful, and in serious cases, patients can have fever, chills and other systemic manifestations, but it will not be accompanied by breast swelling and pain. 2. Malignant lymphoma: it is a malignant disease originated from lymph nodes and lymphatic tissues, which mainly manifests as painless and progressive enlargement of lymph nodes, accompanied by fever, emaciation, liver and spleen enlargement, etc., but it does not cause breast swelling and pain. 3. Breast cancer: Breast cancer belongs to malignant tumor of breast, which can be manifested as breast lumps, accompanied by symptoms of lethargy, fatigue, anemia and other malignant manifestations, and part of the patients can have symptoms of breast distension and pain, and lymphatic metastasis can lead to enlargement of axillary lymph nodes. It is recommended that patients go to the hospital, complete the auxiliary examination, in order to clarify the condition, the professional physician to give appropriate treatment for the condition.