What is the difference between breast cancer and simple lymph?

Cancer versus benign: Breast cancer is a malignant or cancerous process. "lymph" can mean lymphatic swelling or edema. Or you may mean lymph node which can be a benign finding on mammogram or physical examination.

Cancer v. Node: Lymph node is a structure in the body that screens lymph that is being drained from surrounding tissue against infection. Breast cancer is a collection of cells from breast ducts/lobules (usually) that have become immortal and often rapidly proliferative whereby they invade surrounding tissues depriving normal cells the ability to co-exist. Cancer cells may find their way to nearby lymph nodes.

Do u mean "LUMP"?: The only way to definitively differentiate a benign breast lump from a malignant one is by breast biopsy. However, by combination of history, physical exam+/-mammogram+/-ultrasound, we can best assess whether a biopsy is necessary.