Rhabdoid tumour of the kidney – Diagnostics – Overview of Information and Clinical Research

Diagnosing rhabdoid tumour of the kidney in young children requires a combination of imaging tests, biopsies, and genetic analysis. Because these tumours grow rapidly and spread quickly, prompt and accurate diagnosis is essential to start treatment as soon as possible and improve outcomes for affected infants and toddlers.

Introduction: Who Should Undergo Diagnostics

Rhabdoid tumour of the kidney is most commonly found in very young children, particularly infants between 11 and 18 months old. Parents or caregivers should seek medical evaluation immediately if they notice certain warning signs in their child. The most common first sign is discovering a lump or mass in the child’s abdomen, which may be felt during routine care or bathing. Because this type of cancer affects mainly infants and toddlers, the child may not be able to express pain clearly and might only show signs of fussiness or irritability.^[1]^[2]

Other symptoms that should prompt immediate medical attention include blood in the urine, which may appear pink, red, or brown. Some children develop fever without an obvious cause, or show signs of abdominal swelling and distension. Difficulty urinating, unusual sleepiness, decreased appetite, or unexplained weight loss are also concerning signs. Because rhabdoid tumours grow extremely fast and can spread to other parts of the body, symptoms often develop quickly and worsen over just days or weeks.^[1]^[5]

Young infants who present with a combination of fever, abdominal mass, and general unwellness should be evaluated urgently. In some cases, children may have signs related to the tumour pressing on nearby structures, such as breathing difficulties if the tumour is large enough to affect the lungs or diaphragm. Any palpable mass in a young child’s abdomen warrants thorough investigation, as early diagnosis can be critical for planning treatment and understanding the extent of disease.^[2]

⚠️ Important

Because rhabdoid tumours can occur in multiple locations simultaneously, including the brain and kidneys, children diagnosed with a kidney tumour should always have brain and spine imaging performed. Similarly, if a child is diagnosed with a brain tumour of this type, doctors should check for kidney involvement. This comprehensive approach helps identify all affected areas and guides treatment planning.

Classic Diagnostic Methods

When a child presents with symptoms suggesting a possible rhabdoid tumour, healthcare providers begin with a thorough physical examination. The doctor will carefully feel the child’s abdomen to check for masses or swelling, and will ask detailed questions about when symptoms started and how they have progressed. This initial evaluation helps determine which diagnostic tests are needed.^[1]

The first imaging test typically performed is an ultrasound, which uses high-energy sound waves to create pictures of the inside of the body. Ultrasound is painless and does not use radiation, making it ideal for examining young children. During this test, a technician moves a small device over the child’s abdomen, and the sound waves bounce off internal organs and tissues to create images. In rhabdoid tumour of the kidney, ultrasound often reveals a large, irregularly shaped mass arising from the kidney. The tumour may appear as a mixture of solid and fluid-filled areas, sometimes with hemorrhagic regions (areas of bleeding) and small calcium deposits called calcifications.^[5]

After ultrasound identifies a suspicious mass, doctors typically order a computed tomography scan, commonly called a CT scan or CAT scan. This test uses X-rays taken from different angles and combines them with computer processing to create detailed cross-sectional images of the body. A CT scan of the abdomen provides much more detailed information about the size and location of the tumour, whether it has grown into nearby blood vessels, and if lymph nodes are enlarged. The scan can show whether the tumour has invaded the renal vein (the main blood vessel leaving the kidney) or if there are fluid collections around the kidney. CT scans can also detect whether the tumour has spread to other organs such as the lungs or liver.^[2]^[5]

Magnetic resonance imaging, or MRI, may also be used in some cases. MRI uses powerful magnets and radio waves instead of X-rays to create detailed pictures of organs and tissues. This test is particularly useful for examining soft tissues and can provide additional information about the tumour’s characteristics and its relationship to surrounding structures. MRI is especially important when doctors need to evaluate whether the tumour has affected the brain or spinal cord.^[1]

A critical part of diagnosing rhabdoid tumour is obtaining a tissue sample through a procedure called a biopsy. In many cases, the biopsy is performed during surgery to remove the tumour. A surgeon removes a small piece of the abnormal tissue, which is then sent to a specialized doctor called a pathologist. The pathologist examines the tissue under a microscope to look for characteristic rhabdoid cells. These are distinctive large cells with an unusual appearance: they have off-center nuclei (the control center of the cell) and abundant pink-staining material in the cell body called eosinophilic cytoplasm.^[2]^[6]

However, diagnosis based solely on how the cells look under the microscope can sometimes be difficult because the appearance can vary. To confirm the diagnosis with certainty, the tissue sample undergoes additional specialized testing. One of the most important tests looks for changes in a gene called SMARCB1 (which also has other names including INI1, SNF5, and BAF47). This gene normally acts as a tumour suppressor, meaning it helps prevent cells from growing out of control. In nearly all rhabdoid tumours, this gene is mutated or missing. Laboratory tests can detect whether the SMARCB1 protein is absent in the tumour cells, which strongly confirms the diagnosis of rhabdoid tumour.^[2]^[4]^[6]

Because rhabdoid tumours spread rapidly, additional tests are performed to check whether cancer has metastasized (spread) to other parts of the body. A chest CT scan or chest X-ray is essential to look for tumour deposits in the lungs, one of the most common sites where these tumours spread. Brain and spinal cord imaging with MRI is always recommended because a significant percentage of children with rhabdoid tumour of the kidney may also have tumours in the central nervous system. Some children develop synchronous tumours, meaning tumours in two different locations at the same time, such as the kidney and brain.^[4]^[9]

Blood tests are part of the diagnostic workup, though they do not diagnose the tumour directly. A complete blood count checks levels of red blood cells, white blood cells, and platelets. Children with rhabdoid tumour may have anemia (low red blood cells) or low platelet counts. Blood chemistry tests evaluate kidney function and check calcium levels, as some children with this tumour develop elevated blood calcium, a condition called hypercalcemia. Urinalysis, or urine testing, can detect blood in the urine, even when it is not visible to the naked eye.^[5]^[7]

In some cases, doctors may perform a bone scan, which uses a small amount of radioactive material to look for areas where cancer might have spread to the bones. However, there is some debate in the medical community about whether bone scans are routinely necessary for all children with rhabdoid tumour.^[5]

The combination of imaging studies showing a characteristic kidney mass in a very young child, along with microscopic examination revealing rhabdoid cells and laboratory confirmation of SMARCB1 gene changes, establishes the diagnosis. This comprehensive approach helps distinguish rhabdoid tumour from other types of kidney tumours that can occur in young children, such as Wilms tumour or congenital mesoblastic nephroma, which require different treatment approaches.^[5]

Diagnostics for Clinical Trial Qualification

When children are being considered for enrollment in clinical trials studying new treatments for rhabdoid tumour of the kidney, they typically must undergo a standardized set of diagnostic tests. These tests serve multiple purposes: they confirm the diagnosis beyond doubt, determine how far the disease has spread (called staging), establish baseline measurements to track how well treatment works, and ensure the child meets specific criteria that define who can participate in the study.^[2]

Genetic testing of the tumour tissue is especially important for clinical trial entry. Most trials require confirmation that the SMARCB1 gene is altered in the tumour cells. This can be done through several methods. One approach is immunohistochemistry, a laboratory technique where special stains are applied to tissue samples. If the SMARCB1 protein is absent from the tumour cells, the staining will show this loss, confirming the genetic change. More detailed genetic sequencing may be performed to identify the exact type of mutation present. In rare cases where SMARCB1 is normal, testing may look for changes in another related gene called SMARCA4.^[2]^[4]

If a mutation is found in the tumour, doctors often recommend additional genetic testing of the child’s normal, non-cancer cells, usually obtained from a blood sample. This is because in some children, the genetic change is present not just in the tumour but in all cells of the body, indicating an inherited predisposition to develop rhabdoid tumours. Children with these germline mutations (present from birth in all cells) are at higher risk of developing additional tumours and may have family members who carry the same genetic change. Understanding whether a child has a germline mutation can affect eligibility for certain clinical trials and helps determine if family members should undergo genetic counseling.^[1]^[4]

Complete staging workup is mandatory for clinical trial enrollment. This means the child must have comprehensive imaging to document all sites where tumour is present. High-quality CT scans or MRI scans of the abdomen define the size of the primary kidney tumour, whether it has grown into blood vessels, and if lymph nodes near the kidney are enlarged. Chest imaging documents any lung metastases. Brain and spine MRI scans confirm whether tumours are present in the central nervous system. These imaging studies must typically be performed within a specific time window before starting trial treatment, often within two to four weeks, to ensure the information is current.^[4]

Clinical trials may also require specific blood tests performed according to standardized protocols. In addition to routine blood counts and chemistry panels, some trials measure specific substances in the blood that might indicate disease activity or predict treatment response. Kidney function must be carefully assessed because some experimental treatments can affect the kidneys. Liver function tests evaluate whether the liver is working properly, as some chemotherapy drugs are processed by the liver.^[5]

Performance status assessment is another criterion. Doctors evaluate how well the child is functioning overall using standardized scoring systems. This includes assessing activity level, appetite, growth, and overall well-being. Children must typically meet minimum performance standards to safely tolerate intensive treatments being studied in clinical trials.^[12]

Detailed pathology review is often required, with tumour samples sent to specialized reference laboratories where expert pathologists examine the tissue. These central reviews ensure that the diagnosis is accurate and that all children enrolled in a trial truly have the same disease. The pathology report must document specific features of the tumour, including how the cells look, what percentage of different cell types are present, and confirmation of genetic changes.^[6]

⚠️ Important

Participation in clinical trials is voluntary, and families should understand all requirements before deciding whether to enroll their child. The extra tests required for trial enrollment are performed to ensure patient safety and to generate reliable scientific data that can help future children with this disease. Doctors and research coordinators will explain all procedures and answer questions before families make their decision.

Prognosis and Survival Rate

Prognosis

The prognosis for children with rhabdoid tumour of the kidney remains challenging, though outcomes have modestly improved with more intensive treatment approaches. Several factors influence how a child with this disease will do. The age at diagnosis is significant, with very young infants, particularly those under six months, often facing greater challenges. The extent of disease at diagnosis matters considerably: children whose tumour is confined to the kidney and can be completely removed surgically tend to have better outcomes than those whose cancer has already spread to other organs such as the lungs, liver, or brain at the time of diagnosis.^[4]^[12]

The presence of metastases, or cancer spread beyond the kidney, significantly worsens prognosis. Children with stage IV disease (meaning cancer has spread to distant organs) face particularly difficult odds, as these tumours are often resistant to conventional treatments. The location and number of metastatic sites also matter, with brain involvement generally associated with poorer outcomes. Whether the tumour can be completely removed surgically is another critical factor. Complete surgical removal of all visible tumour gives children the best chance, while tumours that cannot be fully removed or that grow back quickly after surgery are much harder to control.^[12]^[17]

How the tumour responds to initial chemotherapy and radiation treatment provides important prognostic information. Tumours that shrink significantly with treatment and do not return for extended periods indicate better prognosis, while those that continue growing despite aggressive therapy or relapse shortly after initial treatment suggest a more aggressive disease course. Children who experience disease relapse face extremely poor outcomes, with very few long-term survivors reported in the medical literature, though rare cases of survival after relapse have been documented.^[17]^[24]

The presence of germline SMARCB1 mutations (genetic changes present in all cells of the body, not just the tumour) may increase the risk of developing additional tumours, which affects long-term prognosis. Some children with inherited mutations develop tumours in multiple locations or experience new tumours years after successful initial treatment. Prompt medical attention and aggressive, multimodal therapy are considered essential for achieving the best possible outcomes.^[1]^[2]

Survival rate

Rhabdoid tumour of the kidney has one of the poorest survival rates among childhood kidney cancers. Published medical literature reports overall survival rates ranging widely depending on disease extent and treatment era, with estimates between 2% and 22% in some studies, reflecting the highly aggressive nature of this disease.^[5]^[17]

Children with localized disease (cancer confined to the kidney without spread) who receive intensive multimodal treatment have survival rates that may exceed 20%, with some centers reporting better outcomes using very aggressive chemotherapy protocols. However, for children with metastatic disease at diagnosis (stage IV), survival rates traditionally remain below 20%, despite intensive treatment. Most children who die from this disease do so within the first one to two years after diagnosis, reflecting how rapidly these tumours can progress.^[4]^[17]

The case report of a three-month-old infant who died just five months after surgical resection despite receiving chemotherapy illustrates the aggressive nature of this cancer and the challenges in achieving long-term survival, even with treatment.^[5]^[17]

It is important to understand that survival statistics are based on groups of children treated in the past, and outcomes for individual children can vary significantly. Ongoing research and clinical trials exploring new treatment approaches offer hope that survival rates will improve in the future. Some children do achieve long-term survival, particularly those with localized disease who respond well to intensive treatment, though these represent a minority of cases.^[12]

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