After removal of an infected spaceous cyst "on the lateral chest wall" an axillary lymph node which was already swollen became bigger and more tender ?

Reactive lymph node: If you had infected " sebaceous cyst" on lateral chest.. it is area of draining lymphatic vessels to axilary nodes( as river tributary) . All bactetia are filtered " cought" in lymph nodes of this area. Normal immune system reaction is swelling,.. inflammation is reaction to infection in area. As infection heals , lymph-nodes pain and swelling resolves.( antibiotics may be needed if severe