Rhabdoid tumors are rare, aggressive cancers that primarily affect babies and young children, requiring prompt medical attention and thorough diagnostic evaluation to determine the best course of action.

Introduction: Who Should Undergo Diagnostics

Parents and caregivers should seek medical evaluation if they notice certain warning signs in their child, particularly in infants and toddlers under three years of age. Rhabdoid tumors most commonly affect babies between 11 and 18 months old, though they can appear at any age during early childhood.^[1] The average age at diagnosis is 15 months.^[2]

Because rhabdoid tumors grow and spread very quickly, symptoms often develop rapidly and worsen over a period of days or weeks. This makes early recognition and prompt medical attention especially important. If your child shows any concerning symptoms, you should consult your local doctor or pediatrician as soon as possible.^[9]

The symptoms that should prompt you to seek diagnostic evaluation depend on where in the body the tumor is growing. For tumors in the abdomen, parents might notice a lump or mass that can be felt through the skin, or the child’s belly may appear unusually swollen or stick out. Blood in the urine, difficulty urinating, or persistent abdominal pain are also warning signs.^[2] Because these tumors occur most frequently in infants who cannot communicate their discomfort clearly, increased fussiness or irritability may be the only early indication that something is wrong.^[15]

For tumors affecting the brain or spinal cord, symptoms include headaches that occur first thing in the morning or headaches that improve after vomiting. Parents may notice unusual sleepiness or low energy levels, loss of balance, lack of coordination, or trouble walking. Nausea and vomiting are common. In babies, an increase in head size may be visible.^[1][9]

Other general symptoms that may appear regardless of tumor location include fever, swollen lymph nodes, decreased appetite, weight loss, and in some cases, difficulty breathing or nerve paralysis.^[1][3] Some children may experience anemia, which is a low red blood cell count, or a low platelet count.^[21]

Diagnostic Methods

When a child presents with concerning symptoms, doctors follow a systematic approach to determine whether a rhabdoid tumor is present. The diagnostic process begins with a thorough evaluation and progresses through increasingly specialized tests.

Initial Evaluation

The first step in diagnosing a rhabdoid tumor involves a comprehensive medical history and physical examination. Your child’s doctor will ask detailed questions about when symptoms started, how they have changed over time, and whether there is any family history of cancer or genetic conditions. During the physical exam, the doctor will carefully check for any lumps or masses, especially in the abdomen, and assess your child’s overall health and neurological function.^[2][19]

The local doctor will typically try to rule out other, more common illnesses first. They may order basic blood tests and urine tests to check for signs of infection, anemia, kidney function, or other abnormalities that might explain the symptoms.^[9] If these initial tests raise concerns or if the symptoms persist, the child will be referred to a cancer specialist called an oncologist, who is a doctor specially trained in diagnosing and treating cancer.^[9]

Imaging Tests

Imaging tests are crucial for visualizing the inside of the body and locating tumors. These tests create pictures that help doctors see the size, location, and extent of any abnormal growths. Several different types of imaging may be used depending on where the tumor is suspected to be.

Ultrasound is often one of the first imaging tests performed. This test uses high-energy sound waves that bounce off internal organs and tissues to create images. Ultrasound is particularly useful for examining the abdomen and kidneys. It is painless and does not use radiation, making it safe for children.^[1][14]

X-rays may be used to get a basic picture of the affected area. While X-rays provide less detail than other imaging tests, they can help identify obvious abnormalities and are quick to perform.^[14]

Computed Tomography (CT) scans, also called CAT scans, provide more detailed cross-sectional images of the body. A CT scanner moves around the child, taking multiple X-ray images from different angles. A computer then combines these images to create detailed pictures that show bones, organs, and soft tissues. Sometimes a special dye called contrast material is injected into a vein before the scan to make certain tissues show up more clearly.^[2][14]

Magnetic Resonance Imaging (MRI) uses powerful magnets and radio waves instead of X-rays to create detailed images. MRI is especially useful for imaging the brain and spinal cord, as it provides excellent detail of soft tissues. Like CT scans, MRI may also use contrast material to enhance the images. The test takes longer than a CT scan, and the child must lie very still inside a tunnel-like machine, which can be challenging for young children.^[14][22]

These imaging tests help doctors get a detailed picture of the tumor’s size and location. However, because rhabdoid tumors in the brain can look very similar to other types of brain tumors on imaging scans, these tests alone cannot confirm the diagnosis. A tissue sample is needed for definitive diagnosis.^[9]

Biopsy and Tissue Analysis

A biopsy is the definitive way to diagnose a rhabdoid tumor. This procedure involves removing a small sample of tumor tissue so it can be examined under a microscope by a specialist called a pathologist, who is a doctor trained to identify diseases by studying cells and tissues.^[2][19]

The biopsy sample is carefully analyzed in a laboratory. Pathologists look for the characteristic appearance of rhabdoid cells, which are large cells with specific features that distinguish them from other cancer cells. These cells look similar to rhabdomyoblasts, which are cells that normally develop into muscles before a baby is born, which is why the tumor is called “rhabdoid.”^[1][7]

Beyond looking at the cells under a microscope, the tissue sample is tested for specific genetic changes. Nearly all rhabdoid tumors have a mutation in a gene called SMARCB1, which is also known by other names including INI1, SNF5, and BAF47. This gene normally helps control cell growth by acting as a tumor suppressor gene, meaning it prevents cells from growing and dividing too rapidly. When this gene is mutated or missing, cells can grow out of control and form tumors.^[2][4][19]

Testing for SMARCB1 mutations is an important part of the diagnostic process because it helps confirm the diagnosis of rhabdoid tumor. In some rare cases, rhabdoid tumors may instead have a mutation in a different gene called SMARCA4, which has a similar function to SMARCB1.^[5][7]

In many cases, especially for tumors in the brain, the surgeon may attempt to remove as much of the tumor as possible during the same procedure used to take the biopsy. This serves both a diagnostic purpose (providing tissue for analysis) and a therapeutic purpose (reducing the amount of cancer in the body).^[9][19]

Additional Diagnostic Tests

Because rhabdoid tumors can spread to other parts of the body, doctors need to determine whether the cancer has remained in one location or has spread elsewhere. This process is called staging. Additional imaging tests may be performed on different parts of the body to check for signs of cancer spread.^[2]

Blood tests may be performed to check overall health and organ function, including liver and kidney function tests. For some children with liver tumors, doctors may check levels of a protein called alpha fetoprotein (AFP), which can be elevated in certain types of liver cancer.^[14]

Genetic Evaluation

As part of comprehensive care, your child may be offered a genetic evaluation to determine whether the gene mutation is present only in the tumor cells or also in the child’s normal cells throughout the body. Most children with rhabdoid tumors have a new genetic mutation that happened spontaneously and was not inherited from their parents. However, some children are born with the mutated gene inherited from a parent, a condition called Rhabdoid Tumor Predisposition Syndrome (RTPS).^[1][8]

Children with RTPS have a higher chance of developing multiple tumors and are often diagnosed at a younger age than children with sporadic rhabdoid tumors. If a child is found to have RTPS, genetic counseling may be recommended for the family. This involves meeting with a trained professional who can explain the inherited condition, discuss the likelihood of passing on the mutated gene to future children, and recommend screening for other family members if appropriate.^[1][8]

Diagnostics for Clinical Trial Qualification

Clinical trials are research studies that test new ways to prevent, find, or treat diseases. Because rhabdoid tumors are so rare and aggressive, and because there is no standard treatment that works well for all patients, many children with these tumors may be offered the opportunity to participate in a clinical trial. The diagnostic tests used to qualify patients for clinical trials are similar to those used for standard diagnosis, but may include additional specialized evaluations.

Confirming the Diagnosis

Clinical trials have strict criteria about who can participate, called eligibility criteria. For rhabdoid tumor trials, one of the most important requirements is confirming that the child truly has a rhabdoid tumor. This typically requires pathology confirmation showing the characteristic rhabdoid cells and, importantly, documentation of SMARCB1 or SMARCA4 gene mutations.^[2][19]

The biopsy or surgical tissue sample must be reviewed by pathologists, and the genetic testing must clearly demonstrate the loss or mutation of the SMARCB1 gene (or less commonly, the SMARCA4 gene). This molecular confirmation is increasingly required for clinical trial enrollment because it ensures that all participants truly have the same type of tumor, which makes the trial results more reliable and meaningful.^[7]

Determining Disease Extent

Clinical trials need to know exactly where the cancer is located and whether it has spread. This requires comprehensive imaging of the entire body. For brain tumors, detailed MRI scans of the brain and spinal cord are typically required. For tumors outside the brain, CT scans or MRI scans of the chest, abdomen, and pelvis may be needed to check for any signs that the cancer has spread to other organs.^[13]

The extent of surgical removal is also an important factor. Clinical trials often categorize patients based on whether the tumor was completely removed during surgery, partially removed, or could not be removed at all. This information helps researchers understand how different treatments work in different situations.^[17]

Assessing Overall Health

Before enrolling in a clinical trial, children undergo tests to assess their overall health and how well their organs are functioning. This is important because some experimental treatments may have side effects that could be dangerous for children whose organs are not working properly.

Comprehensive blood tests are performed to check blood cell counts, liver function, kidney function, and electrolyte levels. Heart function may be evaluated with an electrocardiogram (ECG or EKG), which records the electrical activity of the heart, or an echocardiogram, which uses ultrasound to create moving pictures of the heart.^[12]

Kidney function is particularly important to assess because some chemotherapy drugs can affect the kidneys. Tests may include blood tests to measure substances that indicate how well the kidneys are filtering waste, as well as tests to measure how much urine the child is producing.^[14]

Age and Developmental Considerations

A child’s age is a significant factor in clinical trial eligibility because different treatments may be appropriate or safe for different age groups. Very young infants, particularly those under 6 months old, may not be eligible for certain trials because their developing bodies may not tolerate some treatments. Age is carefully documented as part of the trial enrollment process.^[13][22]

For brain tumor trials, neurological function is carefully assessed. This includes evaluating the child’s ability to move, their alertness, and any symptoms like seizures or changes in behavior. These assessments help determine the child’s baseline condition, which is important for measuring whether the treatment is helping or causing harm.^[22]

Specialized Molecular Testing

Some clinical trials are testing treatments that target specific molecular characteristics of tumors. For these trials, additional specialized testing of the tumor tissue may be required. This might include detailed analysis of which genes are turned on or off in the tumor cells, or testing for specific proteins that the experimental treatment is designed to target.^[12]

Advanced genetic sequencing techniques may be used to create a complete picture of all the genetic changes in the tumor. This information helps researchers understand why some tumors respond to certain treatments while others do not. While this type of testing is not typically part of routine diagnosis, it is becoming more common in research settings and may eventually lead to more personalized treatment approaches.^[12]

Ongoing Monitoring During Trials

Once enrolled in a clinical trial, children undergo regular diagnostic tests to monitor how the tumor is responding to treatment and to watch for any side effects. This typically includes repeated imaging scans at scheduled intervals to see if the tumor is shrinking, staying the same size, or growing. Regular blood tests monitor organ function and blood cell counts throughout treatment.^[12]

The frequency and types of monitoring tests vary depending on the specific trial protocol. Some trials may require weekly blood tests and monthly scans, while others have different schedules. All of this monitoring generates valuable data that helps researchers understand how well the experimental treatment is working and whether it is safe enough to be used more widely in the future.