Clear cell carcinoma (CCC), also sometimes called clear cell cancer, is a rare form of tumor that is characterized by cells that appear pale in color or clear, with solid boundary demarcations under the microscope. These cells tend to be either filled with fluid or glycogen. Clear cell carcinoma can be found in many different types of tumors.

Carcinoma tumors arise from epithelial cells. Epithelial cells make up the surface of the body and cavities. Even though clear cell carcinoma can occur in many different locations, it is recognized as a vaginal and lower urinary tract disease. Most clear cell carcinoma tumors are malignant and are considered to be a high grade cancer, but they often have a high survival rate.

One area this type of cancer is known to affect is the kidney. Clear cell renal carcinoma, also known as renal cell adenocarcinoma (RCA), originates in the renal tubules of the kidney. It is a very common type of kidney tumor; nine out of ten kidney tumors are RCA, and eight out of ten of RCA tumors are clear cell tumors.

Clear cell carcinoma can also be found in breast tumors, the skin, and other locations. It is most often associated with the ovaries, vaginal tract, and uterus. Carcinoma tumors of the ovary are a common form of ovarian cancer. The cancer generates from the epithelial cells that cover the ovary itself.

This type of cancer in the ovaries is also known as clear cell adenocarcinoma and clear cell mesonephroma. W. Schiller called CCC of the ovary clear cell mesonephroma cancer in 1939 because he believed that the structure of the tumor resembled renal tumors. Adenocarcinomas are cancers that start in the glandular tissues that are part of the epithelial tissues.

CCC is common in female patients whose mothers took the drug diethylstilbestrol (DES) during pregnancy. DES is a synthesized non-steroidal estrogen that was prescribed from 1938 to 1971. It was the first synthesized synthetic hormone. Pregnant women were prescribed it in the 1940s as a preventative against miscarriage. The FDA declared in 1971 that the drug was not safe to use during pregnancy, because it was causing a high incidence of heath problems in the children that resulted from DES pregnancies.

The daughters of the women who had taken the drug have a very high incidence of CCC. CCC usually occurs in the late teens and twenties, but it has been known to appear when the women are in their 30s and 40s. It is thought that the hormonal changes during puberty activate the cancer. It is estimated that there are over ten million DES mothers and daughters in the US.