I have a large hard lump behind my knee. it is painless . two years ago i had a mastectomy due to a borderline phyllodes could they ne related ?

Bakers cyst: It that location, behind your knee, a lump is either a baker's cyst or a popliteal artery aneurysm. An ultrasound will quickly and easily give the diagnosis. The lump is not likely to be related to your breast diagnosis, but very important to get a diagnosis.

DOUBTFUL: A painless lump behind the knee may be a bakers cyst, an orthopedic issue. It is not likely to be associated with a phylloides tumour of the breast. Phylloides are not malignant in a classic sense, but have a tendency to local recurrence. I suggest you ask for an ortho consult to examine the knee mass. Good luck.