There are major differences between
tumors in children and adults, viz. the incidence of
tumor types, the predisposition of certain organs and tissues (e.g. sympathetic nervous tissue, kidney, and soft tissues) to develop
tumors, problems related to
tumor classification, and the
biologic behavior of childhood
malignancies, which are usually characterized by high rates of proliferation activity. A large number of new entities, especially in soft tissue
tumors, have been published over the past years, including nodular mesothelial
hyperplasia, which is a
tumor-like lesion derived from peritoneal macrophages; infantile
myofibromatosis, which can mimic
leiomyosarcoma; intermediate grade fibrohistiocytic
tumors, like
dermatofibrosarcoma protuberans-related
giant-cell fibroblastoma, plexiform fibrohistiocytic
tumor and angiomatoid
malignant fibrous histiocytoma displaying evidence of myogeneous differentiation; finally, the high-grade intraabdominal
desmoplastic small cell tumor. With modern methods we can gain better insights into the biology of
tumors. For example,
tumors of the
Ewing's sarcoma family have in common a characteristic t(11; 22)
chromosomal translocation, the
Ewing's sarcoma (EWS) (22q12) gene rearrangement, and the MIC2 gene. The EWS gene rearrangement is not restricted to
tumors of the
Ewing's sarcoma family (classic
Ewing's sarcoma and malignant
peripheral neuroectodermal tumor), however, but occurs in
malignant melanoma of the soft tissue and in intraabdominal
desmoplastic small cell tumor.
Rhabdomyosarcomas (RMS) can be divided into two basic types with different prognoses: embryonal RMS, including botryoid and spindle-cell variants, and alveolar RMS, including the solid variant. The prognosis of alveolar RMS is poorer than that of classic embryonal RMS, mainly due to early
tumor dissemination in alveolar RMS. The prognosis of
neuroblastoma is mainly based on chromosomal and molecular
biologic findings. Structural chromosome 1 abnormalities, double minute chromosomes, homogeneously staining regions, N-myc amplifications, and
DNA diploidy are indications for an unfavorable outcome. Despite progress in childhood solid
tumor pathology, many questions remain open, including those relating to basic chromosomal defects in
germ cell tumors and the obscure nature of
tumor heterogeneity.