Congenital Tumors

Tumors presenting in the newborn period are rare, although pathologists working at busy obstetric or neonatal units can expect to see occasional cases (Isaacs 1997, 2002b). The incidence is around 1 in 12,000 to 1 in 27,500 live births (Moore et al. 2003). Many of these tumors are specifi c to infants or behave differently from their counterparts in older children. Lack of familiarity with neonatal tumors may lead to unnecessarily aggressive therapy or well-intentioned neglect. Some neonatal tumors may appear to be aggressive lesions and yet be benign and, conversely, others look benign but may be fatal if incompletely excised. Most, but not all, childhood neoplasms have been described in the perinatal period. As in children generally, they are often mesenchymal rather than epithelial in his-togenesis, and knowledge of normal human development is often useful. Space limitations prevent this chapter from being comprehensive, so the focus is on the special characteristics of neonatal tumors that infl uence their diagnosis and management, and this chapter also discusses some areas where the study of neonatal tumors is of interest to our understanding of neoplasia in general. Some characteristic lesions not mentioned elsewhere in the text are listed in Table 15.1. Isaacs (1997, 2002; Las Heras and Isaacs 1987) in particular has presented extensive reviews of the subject. Neonatal tumors accounted for 2.6% of all children's tumors in his series, of which 40% were malignant. About 40% of malignant tumors in neonates are evident on the fi rst day of life, and 17% only discovered at autopsy (Campbell et al. 1987). Most malignant congenital tumors present in the fi rst week.

A congenital tumor is one that is present at birth, but it is reasonable to suppose that any tumor presenting in the fi rst 3 months of life is congenital. It is now becoming clear that other childhood tumors, including many leukemias, Wilms' tumors, bronchopulmonary blastomas, and neuroblastomas, appear to arise from cells or lesions that are already abnormal at the time of birth. Children who present with acute leukemia can be found to have identical genetic changes in their leukemia and in the DNA from their Guthrie card or in the leukemia in their monozygotic twin (Greaves 2005). More neonates have these genetic changes than do children who develop leukemia. These studies show that many childhood leuke-mias have precursor cells that have undertaken the initial genetic steps of neoplastic progression at birth, although they do not necessarily progress to malignancy, a situation well described with nephrogenic rests and Wilms' tumors. This then raises the question of why tumors in infants are different from those in adults, which may be partly explained by the time needed for mutations to develop in epithelial tissues for adult tumors to occur and for exposure to mutagenic environmental agents. In other cases, such as Wilms' tumors, the cell of origin is probably the meta-nephric blastema that regresses during development. However, for acute leukemia, for example, the stem cells persist through life and the reasons are less clear but probably relate to the fetal environment and development.