Breast lump

Recently I discovered a lump very high on my breast, almost more between my breast and upper arm.  The location is such that I suspect it would not have been detected my my recent mammogram.  The doctor, despite saying that it's likely a fibrocystic lump, has recommended a repeat mammography and a sonargram, a recommendation which I plan to follow as soon as possible; however, I would like to know if breast cancer develops in such a location?  If not a fibrocystic lump, what are the other possibilities?
Thank you.

[CCF-RN,MSN-JS]

Dear Jeri, Breast cancer can develop in any area that has breast tissue.  We have lymph nodes in this area,  it could possibly be a swollen lymph node.  The mammogram and sonogram may give more information. The physician may then want to take a sample of the lump to examine under the microscope to further determine what it is.