Breast cancer involves the transformation of breast tissue cells into cells that grow uncontrollably. Breast cancer cells can absorb available nutrients resulting in the death of normal tissue, and can metastasize, meaning they spread to other sites in the body. The growth of cancer cells into malignant tumors can cause detectable lumps, either ones that can be felt during a self-exam, or by a doctor; they also may be detectable by X-ray mammography or ultrasound.
Ductal Cell Carcinoma
A lump formed by ductal cell carcinoma occurs when cells that line the ducts of the breasts become cancerous. The ducts allow breast milk that is produced in the lobule cells to travel to the nipple for breast-feeding. Ductal cell carcinoma is the most common type of breast cancer, according to the American Cancer Society. The lump may be in situ, meaning it has not invaded the surrounding breast tissue or metastasized, or invasive, meaning it has spread elsewhere in the breast or in the body.
Lobular Carcinoma
Lobular carcinoma starts in the milk-producing glands of the breast. The American Cancer Society (ACS) reports that lobular carcinoma in situ is sometimes not considered breast cancer because it rarely metastasizes. However, a lump caused by invasive lobular carcinoma is definitely cancer and can spread to other parts of the body. Invasive lobular carcinoma may be harder to detect on a mammogram than invasive ductal carcinoma, according to ACS.
Connective Tissue Tumors
Cancer of the breast connective tissue can also result in a breast lump, though this type of cancer is rare, according to the Mayo Clinic. This type of cancer occurs when cells of the muscles, fat or blood vessels transform into cancer cells. Clinically, this type of cancer is called a sarcoma. One type of lump caused by a connective tissue tumor is a Phyllodes tumor. The University of Rochester Medical Center reports that a Phyllodes tumor is a rapidly growing solid lump that grows from the fibrous epithelial tissue of the breast.
