Small cell, large cell: What do these cancer classifications mean?

Why are some cancers described as small cell and some as large cell? What do these terms mean?

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Mayo Clinic oncologist Timothy Moynihan, M.D., and colleagues answer select questions from readers.

Answer

The terms "small cell" and "large cell" are merely descriptive terms for the appearance of the cancer cells under the microscope. In addition to determining the appearance of the cells, your doctor will also perform tests to determine the size of the cancerous area, how abnormal the cells appear, and if the cancer has spread to the lymph nodes or other organs. While each of these factors is important, classifying a cancer based on its microscopic appearance helps your doctor determine:

The likely course or outcome (prognosis) of the cancer
The most effective treatment for a specific cancer

Common terms used to describe the appearance of cancer cells include:

Clear cell. The inside of the cells appears clear. Examples include some kidney, ovarian and uterine cancers.
Spindle cell. The ends of the cell are narrower at both ends than the center. Examples include some breast, gastrointestinal, muscle or other soft tissue, and skin cancers.
Large cell. The cells are larger than normal cells. An example is lung cancer affecting the bronchioles.
Small cell. The cells are smaller than normal cells. An example is small cell lung cancer, an aggressive cancer that usually spreads to other parts of your body (metastasizes).
Squamous cell. The cells are flat in appearance. Examples include skin cancer or any other type of cancer that starts in the lining of some organs.
Adenocarcinoma. The cells are gland-like in appearance. Examples include some lung, gastric and endometrial cancers.

Other factors that help classify a cancer include:

Area of the body in which the cancer originated, such as the liver or breast. Cancers from certain organs may have a similar appearance. For example, the most common type of kidney cancer is classified as clear cell. On the other hand, breast cancer rarely has a clear cell appearance. So clear cells on a breast biopsy may indicate that the cancer didn't originate in the breast but perhaps spread (metastasized) from another area of the body, such as a kidney.
Type of tissue from which the cancer evolved, including carcinomas and sarcomas. Carcinoma is a cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is a cancer of the bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.