It is a very common skin ailment. However, when this type of cyst occurs on the breast, it is usually cause for a breast cancer screening mammogram. So an epidermoid cyst is a small, palpable bump on the skin usually in a 'dome' shape and appearing as a sore. Oct 14, - Breast cancer is the most common cancer found in women, but most breast lumps are not cancer. So can a woman tell if a breast lump is.