Extensive molecular testing is required when diagnosing pediatric tumors, said Joan Durbin of the department of pediatrics at the Ohio State University College of Medicine at Tuesday’s microbiology-immunology seminar.

The spectrum of pediatric tumors is very different than that of adults.  The tumors that present in children are usually blastomas, rather than carcinomas, which are found primarily in adults. Blastomas are primitive tumors that arise from precursor cells called blasts. Carcinomas, in contrast, arise from epithelial cells that line the structures of the body.

The types of tumors found in pediatric patients vary greatly depending on age, histogenesis, clinical information and antigen expression. Because these factors have such a large impact on the tumor and thus the degree of risk, extensive testing is needed for prognosis, Durbin said.

One of the more important tests is fluorescent in situ hybridization (FISH), a cytogenetic technique that searches for the presence of certain DNA sequences on chromosomes.  This test locates cytogenetic abnormalities and can probe as specifically as a single gene or as broadly as an entire chromosome.

Targeted therapy based on genetic analysis provided by FISH is the goal of tumor biologists such as Durbin.  The reason is that greater specificity of treatment allows for lower doses and consequently reduced morbidity and treatment-related second malignancies.

Second malignancies were shown as a problem when newborn screening was conducted in the nineties.  This survey caught twice as many incidences of tumors as normal screening methods. However, the tumors were not especially threatening. In fact, the screening process failed to discover dangerous cases that generally present after one year.  Consequently, all treatment administered based on this screening method was seen as unnecessary as the tumors found would probably have regressed anyway.

For these reasons, Durbin emphasized the importance of intensive individualized diagnosis techniques.  For instance, every patient that presents with acute lymphoblastic leukemia, the most common pediatric cancer, is enrolled in a trial based on his or her diagnosis.

This allows for a substantially greater information base so that medical professionals can tailor treatment to patients.

One of the major motivating factors behind this customization of treatment is the Childhood Cancer Survivor Study.  This study found that, between 1970 and 1986, treatment caused 75 percent of the morbidity that plagued cancer survivors.  Similarly, occurrences of second malignancies were commonly found at the site that received radiation therapy.

Because of these treatment-related issues, Durbin outlined the multitude of tumor characteristics that are now being factored into childhood prognosis. Screenings for diploid status, tests for the existence of N-Myc, which is a gene commonly associated with neuroblastomas, and the degree of cell differentiation in the tumor are all being taken into account.