Pits on the back are not necessarily malignant tumors or cancer; they may be skin diseases or diseases of the sweat or sebaceous glands. For example, pits can be left behind after a boil breaks down, or after artificially squeezing a sweat tumor or sebaceous mass that has grown on the back, or after a boil breaks down and hardens naturally. Cancers have specific changes, such as forming a mass at the surface of the body and having significant enlargement, causing local pain or causing irritation or compression of peripheral nerves, as well as ulceration and bleeding causing systemic symptoms. For example, malignant tumors on the surface of the body, such as skin cancer, basal cell carcinoma or squamous cell carcinoma, can break down and show ulcerative changes, so the diagnosis of malignant tumors is comprehensive and multifaceted.