|Photomicrograph of cytological smear of Wilms' tumor (nephroblastoma).
In children, solid tumors outside the central nervous system include many types of malignant tumors with different characters and with difference in malignant potential (1).
The most common cancer types are:
- Wilms' tumor
- germ cell tumors
- malignant liver tumors
- non-rhabdo soft tissue sarcoma
- Ewing's sarcoma and peripheral primitive neuroectodermal tumor (PNET)
Neuroblastoma is an embryonal tumor originating from the sympathetic nervous system. Most cases are diagnosed in children < 5 years. The prognosis and treatment depend on the age of the patient, clinical stage, histological differentiation, and biological markers of the tumor (especially n-myc amplification).
Wilms' tumor constitutes 90% of childhood kidney cancer cases and generally has with a good prognosis. Eighty percent of the cases are diagnosed in children < 5 years.
Germ cell tumors originate from primitive germ cell tissue and their malignant behavior depends on the cell that undergoes malignant transformation. Around 50% of the tumors are of low malignant potential. About half of the cases are localized to the gonads, 25% to the sacrococcygeal area, 20% in the central nervous system, and the rest can be found all over the body. Most germ cell tumors, especially the benign behaving tumors, are discovered in the first year of life, but germ cell tumors can be discovered in all age groups.
Two-thirds of liver tumors are malignant. The most commonly are hepatoblastoma and hepatocellular carcinoma (1.8:1).
Sarcomas are malignant tumors occurring in mesenchymal tissue. The main groups are soft tissue sarcomas (rhabdomyosarcoma, 60–70% and non-rhabdomyosarcoma soft tissue sarcomas (NRSTS) 20–30%) and bone sarcomas (osteosarcoma and Ewing's sarcoma).
Rhabdomyosarcoma occurs in primitive mesenchymal cells which have similarities to primitive muscle cells. NRSTS is a group with many different rare tumor types with a large variation in histology and biology.
Osteosarcoma is very rare in small children. The primary tumor occurs often in the metaphysis of the long bones. Two-thirds of pediatric osteosarcomas occur close to the knee.
Ewing's sarcoma and the Ewing's tumor family (ETF) is a clinically heterogenous group of malignant tumors including Ewing's sarcoma, (pPNET) and Askin tumor (ES in the chest wall). These usually occur in bone tissue, but can also occur in soft tissue. The exact histiogenesis is unknown, but it is believed that ETF tumors originate in pluri-potent neuroectodermal stem cells which are found throughout the body.
In Norway in 2012, there were 70 children (0-14 years) diagnosed with solid tumors outside the central nervous system. There were 39 boys and 31 girls (5).
Neuroblastoma and Wilms' tumor constitute about 6% of pediatric cancers, while germ cell tumors constitute 4% and malignant liver tumors make up about 1% of cases.
Soft tissue sarcoma is the most common sarcoma among children and adolescents and constitutes about 8% of pediatric cancer cases. Osteosarcoma occurs primarily in teenagers and about 4-5 children/youth below 20 years are diagnosed every year in Norway. Ewing's sarcoma can occur in children < 10 years, even if it is most common in teenagers. About 2-3 children/youth under 20 are diagnosed every year in Norway.