Malignant Rhabdoid Tumor, from the CureRays guide library.

Malignant rhabdoid tumor is a rare, aggressive cancer of infancy and early childhood that arises in the kidney or other soft tissues; it is defined by loss of the SMARCB1 gene and is treated urgently with surgery, intensive chemotherapy, and radiation, with proton therapy favored to protect a young child's growing body.

What it is.

Malignant rhabdoid tumor is a rare and aggressive cancer that occurs almost entirely in infants and very young children. It is called 'rhabdoid' because some of its cells resemble muscle (rhabdomyo-) cells under the microscope, although the tumor does not actually come from muscle. Rhabdoid tumors can arise in several places: in the kidney (where the tumor is called a malignant rhabdoid tumor of the kidney), in the soft tissues of the body such as the neck, trunk, or limbs, in the liver, and in the brain — the brain form is called atypical teratoid/rhabdoid tumor (ATRT) and is covered in its own guide. This guide focuses on the rhabdoid tumors that arise outside the brain. What ties all of these together is a single defining genetic feature: the loss of a gene called SMARCB1 (also known as INI1), or, less commonly, a related gene called SMARCA4. This loss is found in nearly every rhabdoid tumor and is how the diagnosis is confirmed. Importantly, in a meaningful share of children the loss is present in every cell of the body (a germline change), which creates a 'rhabdoid tumor predisposition syndrome' and a risk of more than one tumor; for this reason genetic testing and counseling for the child and family are an essential part of care. Rhabdoid tumors grow and spread quickly and most often affect children under three, so treatment is urgent and intensive. Because the cancer is so aggressive and these patients are so young, care is highly specialized and combines several treatments: surgery to remove the tumor when possible, intensive multi-drug chemotherapy (sometimes including very high-dose chemotherapy with stem-cell rescue), and radiation therapy. Treating a child this young is a careful balancing act between giving enough therapy to control a fast-moving cancer and protecting a developing body, which is why proton therapy — a form of radiation that concentrates dose on the target and spares surrounding growing tissue — is often favored, and why these children are best treated at specialized pediatric cancer centers, frequently within clinical trials.

How radiation treats it.

Radiation therapy treats malignant rhabdoid tumor by delivering focused beams of energy that damage the DNA inside tumor cells so they can no longer grow and divide. Because rhabdoid tumors are fast-growing and aggressive, radiation is an important part of controlling the cancer in the area where it started and at sites where it has spread, working alongside surgery to remove the tumor and intensive chemotherapy to treat disease throughout the body. The central challenge is that these patients are usually infants and toddlers, whose organs, bones, and especially brains are still developing and are more vulnerable to the long-term effects of radiation. Treatment is therefore a careful balance: enough radiation to control a dangerous cancer, delivered as precisely as possible to protect the growing child. This is exactly where proton beam therapy is so valuable. Unlike standard X-ray (photon) radiation, which passes all the way through the body and deposits dose both before and beyond the target, a proton beam releases most of its energy at a set depth — right in the tumor — and then stops. That means little or no radiation reaches the healthy tissue beyond the tumor, sparing nearby growing organs and lowering the risk of long-term side effects and of radiation-related second cancers later in life. For these reasons, proton therapy is often favored for young children with rhabdoid tumors when it is available. When protons are not used, intensity-modulated radiation shapes photon beams tightly around the target to achieve a similar sparing of surrounding tissue. The radiation is usually directed at the tumor bed and any nearby areas of spread (involved-field), and the field, dose, and timing are carefully tailored to the child's age and to how the tumor has responded to chemotherapy and surgery. If the cancer has seeded the brain or the spinal fluid, radiation may be extended to the brain and spine, but this is done selectively because of its effects on the developing nervous system. Throughout, the goal is to give this aggressive cancer the strongest possible local control while protecting as much of the child's future development as treatment allows.

The ways we can treat it.

Proton beam radiation therapy. Protons deposit most of their energy directly in the tumor and stop, delivering little dose beyond it; this concentrates treatment on the target while sparing a very young child's growing organs, bones, and brain, lowering the risk of long-term side effects and second cancers.

Focal (involved-field) radiation. Radiation aimed at the tumor bed and any nearby areas of spread, shaped tightly to the target, controls residual microscopic disease after surgery and chemotherapy while limiting exposure of healthy tissue.

Intensity-modulated radiation (IMRT). When protons are not used, IMRT shapes photon beams tightly around the target to spare surrounding organs — useful for tumors in complex locations in the abdomen, neck, or trunk.

Craniospinal / brain radiation for spread. If the cancer has seeded the brain or spinal fluid, radiation may be directed at the brain and spine; this is used selectively and tailored to the child's age because of its effects on the developing nervous system.

Questions we hear often.

Why does my child need genetic testing? Nearly all rhabdoid tumors are caused by loss of a gene called SMARCB1 (sometimes SMARCA4). In a meaningful share of children, that loss is present not just in the tumor but in every cell of the body — a change present from birth called a germline mutation. Children with a germline change have a 'rhabdoid tumor predisposition syndrome,' which raises the risk of developing more than one rhabdoid tumor and can sometimes be inherited. Genetic testing tells the team whether your child has this syndrome, which guides closer surveillance, and genetic counseling helps the family understand the risk to your child and to relatives. It is an essential part of caring for any child with a rhabdoid tumor.

Why is proton radiation often recommended for my child? Rhabdoid tumors occur in very young children whose organs, bones, and brains are still developing and are more sensitive to the long-term effects of radiation. Proton therapy delivers most of its energy directly in the tumor and then stops, so very little radiation reaches the healthy tissue beyond it. Compared with standard X-ray radiation, this spares more of a young child's growing tissue and lowers the risk of long-term side effects and of radiation-related second cancers later in life. When it is available and appropriate, proton therapy lets the team give the tumor the strong radiation it needs while protecting as much of your child's future development as possible.

Why is treatment so intensive and urgent? Malignant rhabdoid tumors are among the most aggressive childhood cancers — they grow and spread quickly, including to the brain and spinal fluid, and they most often affect children under three. Because of this, treatment usually starts urgently and combines several powerful tools at once: surgery to remove the tumor when possible, intensive multi-drug chemotherapy (sometimes very high-dose chemotherapy with stem-cell rescue), and radiation. This intensive, coordinated approach gives the best chance of controlling a fast-moving cancer. These children are best cared for at specialized pediatric cancer centers, often within clinical trials testing newer, more effective and better-targeted treatments.

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