A breast cancer cell needs to divide and multiply 30 times before it grows into a breast lump that is about 1 cm in diameter and more visible. This process, which takes 2-3 years, during which time the lump cannot be felt on the surface of the breast because the cancerous tissue is too small, despite the fact that the patient already has breast cancer. There are also some breast cancers where the cancer cells are very scattered and do not gather, and we cannot feel the lumps. Clinically, breast cancer that cannot be detected by physical examination is called “unpalpable breast cancer”. In recent years, as women become more aware of breast cancer, more and more women are undergoing mammograms and the number of patients with unpalpable breast cancer is increasing year by year. In some famous hospitals in China, patients who cannot find a lump account for about 10% of operable breast cancer patients, while in some economically developed countries, patients who cannot find a lump account for 30%-40% of operable breast cancer patients. Since the majority of breast cancers that cannot be detected are early-stage breast cancers, the proportion of patients with breast cancers that cannot be detected is an indirect reflection of the level of early diagnosis of breast cancer in a country or region. Although breast cancer that cannot be felt as a lump cannot be palpated, readers need not worry as there are many methods that doctors can use to detect, diagnose and treat this tumor. Among them, mammography is internationally recognized as the most common and effective method. Mammograms can “catch” many breast cancers before they form a lump and “nip them in the bud” through surgery. Available data has confirmed that mammograms every one or two years in normal women over the age of 40 or 50 will reduce their breast cancer mortality rate by a relative 30%. Some breast cancers that cannot be palpated may not be palpable but may have other signs, such as nipple discharge; nipple erosion with itching, like eczema; and enlarged lymph nodes in the armpits. In addition to mammography, smear tests for nipple discharge, scraping of the nipple erosion, and puncture biopsy of enlarged lymph nodes can help the doctor make a definitive diagnosis. The widespread implementation of mammography and the puncture biopsy of suspicious lesions has made it possible to detect many patients with early stage breast cancer who cannot feel a lump, and will help to further improve the level and effectiveness of breast cancer treatment.