Epidemiology and Dysontogenetic Theory
Although malignant neoplasms (cancer) in children are significantly less common than in adults (about 2% of the total oncology burden), they remain a leading cause of childhood mortality. In developed countries, they account for 10% of deaths, placing oncology second only to accidents.
The foundation of pediatric oncology remains the dysontogenetic theory, proposed by Julius Cohnheim back in 1902. According to this theory, tumors develop from embryonic cell rests due to impaired normal tissue development. While such tumors are rare in adults, dysontogenetic neoplasms account for up to 85% of all malignancies in infants under 1 year of age.
In medical practice, two criteria are still used to define a "congenital tumor":
- The lesion manifests within the first year of life.
- The lesion is diagnosed at birth and strictly within the first 3 months.
Association with Malformations and Genetics
Oncogenesis and teratogenesis (the formation of malformations) in children go hand in hand. On average, 30% of patients with tumors have concomitant developmental anomalies. There are typical clinical patterns:
- Wilms tumor (nephroblastoma) and hepatoblastoma are extremely frequently accompanied by hemihypertrophy—asymmetric enlargement of one half of the body, limbs, or face.
- Central nervous system neoplasms are frequently combined with brain malformations.
- Gonadal tumors accompany genital anomalies.
Genetic factors play a colossal role in the development of pediatric tumors. Science knows more than 100 syndromes with hereditary predisposition. Classic examples of proven hereditary tumors include retinoblastoma, nephroblastoma, and neuroblastoma.
Tumor-Like Lesions: Hamartomas and Choristomas
In pediatric pathology, it is critically important to distinguish true neoplasms from developmental anomalies, although the boundary between them is often blurred.
Hamartoma (from Greek hamartia — error) is a nodular defect of embryonic development. It consists of the same tissue components as the organ in which it is located, but is characterized by a chaotic arrangement of cells and altered differentiation. This is a borderline state between a malformation and a neoplasm. Debates regarding the classification of certain lesions persist: some researchers consider hemangiomas, lymphangiomas, liver adenomas, and cardiac rhabdomyomas to be hamartomas, while others classify them as true tumors.
Choristoma is a tumor-like nodule arising from choristia (heterotopia). Choristia (from Greek choristos — separated) represents a patch of completely normally formed tissue that "got lost" during embryogenesis and ended up in an atypical anatomical location.
Benign Tumors of Childhood
In children under 14 years of age, more than 80% of all neoplasms are benign. Fibromas, teratomas, lymphangiomas, and hemangiomas lead the list.
Hemangioma (capillary, cavernous, or mixed) most commonly affects the skin of the head, neck, and trunk. It has a specific dynamic: rapid growth in the first months of life, cessation of growth by 1–3 years, and spontaneous involution by 5 years. On immunohistochemistry (IHC), such involuting forms show a positive reaction for the endothelial marker GLUT-1. However, progressive variants with infiltrative growth and recurrence also occur.
Special attention should be paid to associated syndromes:
- Kasabach-Merritt phenomenon: a severe complication where consumption coagulopathy (massive thrombosis) develops within a giant hemangioma, leading to thrombocytopenic purpura.
- von Hippel-Lindau disease: a hereditary disorder manifested by multiple vascular tumors.
Lymphangioma is usually detected before age 3. Its clinical danger directly depends on localization: superficial forms are relatively safe, whereas deep ones (in the axillary regions, mediastinum, retroperitoneum, or deep neck spaces) pose a serious threat.