Morphology of neuroblastoma

One of the distinctive features of neuroblastoma is its ability to spontaneously regress, reminiscent of the reverse development of the sympathetic nervous system during embryogenesis. Sympathetic chromaffin paraganglia arise early in embryonic development in the adrenal medulla. By the eighth week of embryogenesis, the hormonally active parenchymatous cells of the adrenal system reach large sizes, and by the time of birth they have sharply decreased.

Another characteristic feature of neuroblastoma is its ability to differentiate in vitro under the influence of various factors (retinoic acid, nerve tissue growth factor, papaverine). At the same time, in vivo the tumor is characterized by extremely aggressive growth and rapid metastasis.

Screening studies of neuroblastoma have revealed a multiple increase in the frequency of this tumor in infants in the first six months of life. This discrepancy with the registered incidence is explained by the phenomenon of spontaneous regression of neuroblastoma in most cases. Regression usually occurs with certain biological characteristics of the tumor: triploid chromosome set, absence of amplification of the N MYC gene and abnormalities of the first chromosome (loss of the short arm). The absence of telomerase expression and the neurotrophin receptor TRK-A is also associated with the possibility of spontaneous tumor regression.

Morphology of neuroblastoma

Histological diagnosis of neuroblastoma can present significant difficulties due to the morphological similarity of this tumor with primitive neuroectodermal tumors, lymphomas, and rhabdomyosarcoma.

Tumor cells in neuroblastoma are similar to embryonic neuroblasts of sympathetic tissue. Microscopically, the tumor is represented by small round cells-neuroblasts with large nuclei and a narrow rim of cytoplasm. Three main components can be distinguished in the tumor tissue - neuroblastomatous, ganglioneuromatous and intermediate. The predominance of one or another component determines the degree of differentiation of neuroblastoma. There are undifferentiated (all tumor cells are neuroblasts), low-differentiated (ganglionic differentiation is noted in less than 5% of cells) and differentiated (more than 5% of cells have signs of differentiation) types of neuroblastoma. The prognosis is most favorable for the latter type of tumor.

The integrated classification (1986) is convenient for determining the prognosis in clinical practice. This classification correlates such indicators as the patient's age and histological features of neuroblastoma (the degree of neuroblast differentiation, the severity of the stromal component, the mitosis/karyorrhexis index). According to this classification, the prognosis is most favorable with a combination of a well-differentiated tumor type and a child's age of less than 1 year.

Molecular genetic aspects of neuroblastoma

Currently, some genetic abnormalities are known that are characteristic of neuroblastoma and determine the prognosis of the disease. The most significant genetic abnormality is amplification of the N MYC gene. Regardless of the patient's age, detection of this abnormality has an unfavorable prognostic value. Amplification of N MYC is often combined with deletion of the short arm of chromosome 1 and an increase in the long arm of chromosome 17. The latter aberration itself has an unfavorable prognostic value.

Hyperploid chromosome set in tumor cells is associated with a favorable prognosis, especially in children of the first year of life. Increased expression of the neurotrophin receptor gene-TRK-A is another favorable prognostic sign of neuroblastoma.

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