Clear Cell Sarcoma of the Kidney, from the CureRays guide library.

Clear cell sarcoma of the kidney is a rare childhood kidney cancer known for spreading to bone; it is treated with surgery, intensive chemotherapy, and radiation, and modern combined treatment has greatly improved survival.

What it is.

Clear cell sarcoma of the kidney (CCSK) is a rare childhood kidney cancer, distinct from the much more common Wilms tumor and from the clear cell sarcoma that occurs in soft tissue of adults. It is the second most common malignant kidney tumor of childhood, usually diagnosed in toddlers and young children, and it is sometimes called the 'bone-metastasizing renal tumor of childhood' because of its notable tendency to spread to bone — though it can also spread to the brain, lungs, lymph nodes, and other sites. Many cases carry a specific genetic change (an internal duplication in the BCOR gene) that helps confirm the diagnosis. Because CCSK is aggressive, it is treated with intensive, coordinated, multimodality therapy. Surgery to remove the affected kidney (nephrectomy) is combined with chemotherapy that includes doxorubicin, and radiation is given to the tumor bed for most patients. Children are treated on pediatric oncology protocols, typically through cooperative groups such as the Children's Oncology Group, which has steadily improved outcomes. With modern combined treatment, the great majority of children with localized disease are cured, and even children with spread can do well. Because relapses — including late ones in bone and brain — can occur, long-term follow-up is important.

How radiation treats it.

Radiation damages the DNA inside cancer cells so they can no longer divide and survive, while healthy cells repair themselves more effectively. In clear cell sarcoma of the kidney, radiation is given to the area where the tumor was removed — and to sites of spread, such as bone — to lower the chance the cancer comes back, working alongside surgery and chemotherapy. Because the patients are young children whose bodies are still growing, radiation is planned very carefully to use the lowest effective dose and to shield developing tissues; in some centers proton therapy is used because it can spare healthy organs near the treatment area. Radiation is given as short, painless daily sessions and leaves no radioactivity in the child's body, so the child remains safe to be around family and other children. Combined with surgery and chemotherapy, radiation is part of the modern treatment that has greatly improved survival.

The ways we can treat it.

Surgery. Removal of the affected kidney (nephrectomy) with lymph-node sampling removes the bulk of the tumor and provides tissue for diagnosis and staging.

Chemotherapy. Combination chemotherapy that includes doxorubicin treats the whole body, addressing this tumor's tendency to spread and substantially improving cure rates.

Radiation. Focused radiation to the tumor bed (and to sites of spread such as bone) lowers the chance of recurrence; in young children, careful planning protects growing tissues, and proton therapy may be used to spare developing organs.

Questions we hear often.

How is this different from Wilms tumor? Clear cell sarcoma of the kidney is a separate, rarer childhood kidney cancer that is more aggressive than Wilms tumor and has a notable tendency to spread to bone. It carries a different genetic change and is treated with more intensive chemotherapy that includes doxorubicin, plus radiation. Telling the two apart on pathology is important because the treatments differ.

Why is radiation used in such a young child? Radiation to the tumor bed lowers the chance the cancer returns locally and is part of the combined treatment that has greatly improved survival. In young children, the radiation is carefully planned at the lowest effective dose, and techniques such as proton therapy can protect growing tissues. Your child's team will explain how they minimize long-term effects.

What is the outlook? Much better than it used to be. With modern combined treatment — surgery, intensive chemotherapy, and radiation — the great majority of children with localized clear cell sarcoma of the kidney are cured, and even children with spread can do well. Because late relapses can occur, long-term follow-up is part of the plan.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.