Understanding a Childhood Cancer Pathology Report

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A pathology report is the document that describes what was found when a sample of tissue from your child was examined under a microscope by a pathologist. For a child with a tumor, this report carries the diagnosis, and it usually carries the test results that decide how the tumor will be treated. It is written for the medical team rather than for families, which is why so much of it is difficult to read.

Childhood tumors are not smaller versions of adult tumors. They start in different cells, carry different genetic changes, and are treated with different plans. This article explains how a childhood cancer pathology report is put together, what each part of it describes, and why it differs from an adult report.

Why are childhood tumors different from adult tumors?

Most tumors in adults grow from tissue that has finished developing, after many years of gradual cell damage. Most tumors in children grow from tissue that is still developing. This is the single most important difference, and it explains much of what appears on a childhood cancer pathology report.

Because these tumors come from developing tissue, they carry names that do not appear in adult cancer care. Words ending in “blastoma,” such as neuroblastoma, nephroblastoma, and medulloblastoma, describe tumors made of cells that look like the immature cells of a growing organ. Children also develop sarcomas, leukemias, and lymphomas far more often than the carcinomas that make up most adult cancer.

Childhood tumors also carry fewer genetic changes than adult tumors. An adult lung or colon cancer may contain thousands of changes built up over decades. A childhood tumor often has one main change, sometimes a single fused gene, driving the whole tumor. Most of these changes come from random errors during rapid cell division in normal growth. The exposures that matter in adult cancer, such as tobacco and sun damage, have little role here.

One practical consequence matters most. Survival figures, treatment descriptions, and risk factors written for adults do not apply to your child, even when the tumor has a similar name. A rhabdomyosarcoma in a four-year-old and a sarcoma in a seventy-year-old are managed by different teams using different plans.

Which cancers are most common in children?

Childhood cancers are uncommon compared with adult cancers, and the mix of diagnoses is very different. Knowing where your child’s tumor sits in that mix can make an unfamiliar name on the pathology report easier to place.

Leukemias. Roughly a quarter to a third of childhood cancers. Acute lymphoblastic leukemia is the single most common diagnosis, followed by acute myeloid leukemia.
Brain and spinal cord tumors. Roughly a fifth to a quarter. These include medulloblastoma, pilocytic astrocytoma, ependymoma, and diffuse midline glioma.
Lymphomas. Roughly one in ten, and a larger share in teenagers, where Hodgkin lymphoma becomes one of the most common cancers of all.
Solid tumors of the body. Neuroblastoma, nephroblastoma (Wilms tumor), rhabdomyosarcoma, osteosarcoma, Ewing sarcoma, retinoblastoma, and germ cell tumors make up most of the remainder.

Outcomes vary widely between these diagnoses, and averages across all childhood cancers will not tell you much about your own child. The oncology team can give you figures that apply to your child’s specific diagnosis, stage, and test results, and those figures are the ones worth asking about.

How is a childhood tumor diagnosed?

A pathologist diagnoses a childhood tumor by examining tissue or cells from the tumor under a microscope. Imaging can show that a mass is present and where it is, but it cannot give the diagnosis on its own. Almost every childhood cancer pathology report begins with a sample obtained in one of three ways.

For a solid tumor, a needle or surgical biopsy removes a small piece of the mass. For a suspected leukemia, a bone marrow biopsy and aspiration sample the marrow inside the hip bone. For some tumors, the surgeon removes the whole mass at the first operation, and the pathologist examines the entire specimen.

Under the microscope, the pathologist looks at the size, shape, and arrangement of the tumor cells. Many childhood tumors look similar at this stage, because they are all made of small cells with very little cytoplasm around the nucleus. Reports sometimes describe this appearance as a small round blue cell tumor, which is a description rather than a diagnosis. Distinguishing between possibilities requires additional tests, which is why a childhood tumor is rarely diagnosed from the microscope alone.

Immunohistochemistry is usually the next step. This test uses antibodies to detect specific proteins inside the tumor cells, and each result is reported as positive or negative. A pattern of results points toward one tumor type and away from others. For leukemias and lymphomas, flow cytometry does similar work by measuring proteins on large numbers of individual cells at once. Genetic testing then confirms the diagnosis in many cases.

What is on a childhood cancer pathology report?

A childhood cancer pathology report is organized in sections, and the same sections appear whether the tumor was found in the brain, the kidney, the bone, or the bone marrow. Not every report contains every section, because a needle biopsy answers fewer questions than a complete surgical specimen.

Specimen description. Also called the gross description. It records what the laboratory received, including the size and appearance of the tissue and how it was sampled.
Diagnosis. The short section naming the tumor. This is the line the oncology team acts on, usually at the top or bottom of the report.
Microscopic description. What the pathologist saw under the microscope. This section uses the most technical language and is written for other physicians.
Immunohistochemistry. The list of stains performed, each with a positive or negative result. These results explain how the diagnosis was reached.
Molecular and genetic results. Fusion genes, gene amplification, mutations, and, in brain tumors, methylation profiling. In children,n these results often carry more weight than anything else on the report.
Histology or grade. Present for some childhood tumors and absent for others, for reasons explained in the staging section below.
Margins. Reported when the whole tumor was removed. A negative margin means no tumor cells were seen at the cut edge of the tissue.
Lymph nodes. Reported when nodes were removed. The report gives the number examined and the number containing tumor.

Some results arrive after the first version of the report is issued. When that happens, the pathologist adds an addendum, and it becomes part of the final report. A report marked pending or awaiting additional testing is not a report that has gone wrong.

Why is molecular testing so important in children?

Molecular testing looks for changes in the genes inside the tumor cells rather than at the appearance of the cells themselves. In childhood tumors, these results often define the diagnosis, and they frequently matter more than the size or the location of the tumor. This is one of the largest differences between a childhood cancer pathology report and an adult one.

These reports include several kinds of results.

Fusion genes. Two genes join together and produce a protein that drives the tumor. Examples include EWSR1-FLI1 in Ewing sarcoma and PAX3-FOXO1 in alveolar rhabdomyosarcoma. The presence or absence of a fusion can change the diagnosis and the treatment plan.
Gene amplification. A gene is present in many extra copies. MYCN amplification in neuroblastoma is the best-known example, and it places the tumor in a higher-risk group.
Mutations. A single change in the letters of a gene. Some mutations define a diagnosis outright, such as the H3 K27 change in diffuse midline glioma.
Methylation profiling. A test used mainly for brain tumors. It reads chemical marks on the DNA and compares the pattern with thousands of known tumors to confirm the type and subgroup.
Chromosome studies. A karyotype or related test that counts and inspects the chromosomes, used most often in leukemia.

Larger panels that read many genes at once, called next-generation sequencing, are now used routinely in pediatric oncology. These results are almost always somatic, meaning they are present only in the tumor cells and not in the rest of your child’s body.

How are childhood tumors staged and grouped?

Staging describes how far a tumor has spread. Most adult cancers are staged with the TNM system, which combines tumor size, lymph node involvement, and distant spread. Most childhood tumors are not, and this surprises many families who have read about staging elsewhere.

Instead, each childhood tumor type has its own system, built around what actually predicts outcome for that tumor.

Nephroblastoma (Wilms tumor). Staged by the Children’s Oncology Group system, and separately described as favorable histology or anaplastic histology.
Neuroblastoma. Grouped by the International Neuroblastoma Risk Group system, which uses imaging features, age, MYCN status, and the appearance of the tumor cells.
Rhabdomyosarcoma. Given both a stage and a surgical grouping that reflects how much tumor was removed at the first operation.
Lymphomas and leukemias. Described by the extent of involvement and by the results of bone marrow and spinal fluid testing rather than by tumor size.
Brain and spinal cord tumors. Assigned a World Health Organization grade from 1 to 4 based on tumor type and molecular findings, without a TNM stage.

Grade is also used differently in children. Several childhood tumors are treated as high grade by definition, so no grade is reported, while others are described by histology categories such as favorable or unfavorable. A report with no grade on it is not an incomplete report.

Why is the report taking so long?

Waiting for a childhood cancer pathology report is one of the hardest parts of the process, and these reports frequently take longer than families expect. The delay usually means the work is thorough, not that something has gone wrong.

Several steps add time. Immunohistochemistry adds a day or more for each round of stains, and a difficult childhood tumor may need two rounds. Genetic tests are often sent to a specialized laboratory and can take one to three weeks. Bone specimens must be treated with acid to soften them before they can be cut, which adds several days on its own.

Childhood tumors are also reviewed more often than adult tumors. Because they are rare, slides are often sent to a pathologist who specializes in children’s tumors or to a national reference center. Some cooperative group treatment plans require this review before treatment begins. Your child’s team can tell you which tests are still outstanding and roughly when each is expected.

What does it mean if treatment is on a protocol or a clinical trial?

Once the childhood cancer pathology report is complete, the findings on it are used to assign your child to a risk group and a treatment plan. Most children with cancer in North America and Europe are treated on a protocol developed by a cooperative research group, and many of these protocols are also clinical trials.

This is standard practice in pediatric oncology, not a last resort. Childhood cancers are rare enough that no single hospital treats many cases. Hospitals pool their experience through shared protocols, and this is a large part of why survival has improved substantially over the past several decades. A trial in this setting usually compares the current best treatment with a version that is expected to be either more effective or less toxic.

The pathology report feeds directly into this assignment. The tumor type, molecular results, stage or group, and margins together determine the risk group, and the risk group determines how intensive the treatment will be. This is why a single test result can change the plan, and why the team may wait for a pending result before starting.

Could my child’s tumor be part of an inherited condition?

Inherited cancer predisposition is more common in children than in adults. Studies that sequence the normal DNA of children with cancer find an inherited condition in roughly 8 to 10 percent. The comparable figure in adults is about 5 percent. For this reason, pediatric oncology offers genetic testing and genetic counseling far more often.

Some diagnoses prompt this testing on their own, regardless of family history. Retinoblastoma, adrenocortical carcinoma, choroid plexus carcinoma, rhabdoid tumors, and pleuropulmonary blastoma are examples where a specific inherited syndrome is common enough that testing is recommended for every child. Other reasons to test include more than one cancer in the same child, an unusual cancer for the child’s age, or a strong pattern of cancer in the family.

This kind of testing differs from molecular testing done on the tumor itself. Tumor testing looks at changes present only in the tumor cells. Inherited testing looks at the DNA your child was born with, which is present in every cell and can be passed down through a family. A change found in the tumor is not by itself evidence of an inherited condition. You can read more in our article What is a hereditary cancer syndrome?

How do I get a copy of the report and ask questions about it?

Families are entitled to a copy of a child’s pathology report, and having the report in front of you makes conversations with the team more useful. You can ask the oncologist, the surgeon, or the hospital’s medical records department, and in many places the report also appears in an online patient portal.

A few things are worth knowing before you read it. The report was written for physicians and will contain terms that have no plain-language equivalent. The diagnosis line matters most, and the microscopic description is what families find most alarming and least useful. If the diagnosis was made at one hospital and your child is being treated at another, ask whether the slides have been reviewed at the treating center. The reviewing pathologist sometimes issues a report of their own.

Second opinions on pathology are routine in this setting and are not a criticism of anyone. If you want one, your child’s oncologist submits the request and arranges for the slides and blocks to be sent to the reviewing pathologist.

Questions to ask your doctor

What is the exact diagnosis on my child’s pathology report?
Is this a tumor that occurs mainly in children, and does that change how it is treated?
Which tests were used to confirm the diagnosis, and are any still pending?
Were any fusion genes, mutations, or gene amplifications found in the tumor?
Does my child’s tumor have a grade or a histology category, and what does it mean?
Which staging or grouping system applies to this tumor, and what stage or group is my child?
Was the whole tumor removed, and were the margins negative?
Were any lymph nodes examined, and did any contain tumor?
Which risk group has my child been assigned to, and what determined it?
Has a pathologist who specializes in children’s tumors reviewed the slides?
Is treatment being given on a protocol or a clinical trial, and what does that involve?
Should my child have genetic testing for an inherited condition, and should other family members be tested?
What are the outcomes for children with this specific diagnosis and risk group?
How do I get a copy of the report, and who can go through it with me?