Metastasis and Staging of Neuroblastoma
Neuroblastoma has a high propensity for early dissemination. The frequency of metastasis directly correlates with the patient's age: metastases are found in 50% of cases in children under one year of age, and in 70% of older patients. Typical metastatic sites include lymph nodes, bone marrow, bone, liver, and subcutaneous adipose tissue.
To assess the extent of the disease, the international staging system based on the pathological examination of resected tissues is used:
- Stage 1: The tumor is localized within the organ of origin, completely excised, with no regional lymph node involvement.
- Stage 2A: The tumor extends beyond the organ of origin, but remains unilateral and does not cross the midline. Grossly complete resection may or may not be achieved; negative regional lymph nodes.
- Stage 2B: Unilateral tumor of any size with complete or incomplete resection, accompanied by ipsilateral regional lymph node involvement.
- Stage 3: Unresectable tumor crossing the midline (with or without regional lymph node involvement), or unilateral tumor with contralateral regional lymph node involvement, or midline tumor with bilateral regional lymph node involvement.
- Stage 4: Dissemination with distant metastases to distant lymph nodes, bone marrow, liver, skin, and/or other organs.
- Stage 4S: A unique variant occurring exclusively in infants under 1 year of age. The primary tumor is stage 1 or 2, but with metastatic dissemination restricted to the skin, liver, and bone marrow.
Diagnosis and Prognostic Factors in Neuroblastoma
Diagnosis is based on clinical presentation and morphological verification. Cytogenetic and biochemical tests are auxiliary. However, 90% of patients show elevated blood levels of catecholamines. In clinical practice, the gold standard is the assessment of 24-hour urinary excretion of their metabolites — homovanillic acid (HVA) and vanillylmandelic acid (VMA).
Prognostication is based on the Shimada classification, which takes into account histological grading, proliferation and apoptosis indices, patient age, and disease stage. The most favorable prognosis is observed in children under 1 year of age (85–90% survival regardless of stage) and in stages 1 and 2 (up to 98%). An age older than one year and the presence of distant metastases critically reduce survival (to less than 10%).
Genetic Markers:
- Deletion of the short arm of chromosome 1 (distal to p32): leads to the loss of a tumor suppressor gene, associated with an unfavorable prognosis.
- N-myc and N-ras amplification: associated with a poor prognosis (up to 300 copies of N-myc in disseminated disease). It is essential to consider both copy number and expression levels.
- Ploidology: hyperdiploidy worsens the prognosis, while near-triploidy/aneuploidy improves it.
- Trk expression: high levels of nerve growth factor receptor stimulate differentiation into mature ganglion cells and increase survival.
Elevated serum markers—neuron-specific enolase (NSE), lactate dehydrogenase (LDH), and ferritin—are also poor prognostic indicators.
Retinoblastoma: Etiology and Genetics
Retinoblastoma is a malignant neuroepithelial neoplasm of the retina, accounting for 2.5–4.5% of all pediatric malignancies (1 in 20,000 live births). It manifests predominantly in the first 3 months of life (mostly diagnosed before age 4). A unique feature of the tumor is its capacity for spontaneous regression.
Two clinical forms exist:
- Familial (hereditary): accounts for about 50% of cases, characterized by multifocal and bilateral involvement.
- Sporadic: always monofocal and unilateral.
The foundation of pathogenesis is mutation of the RB1 tumor suppressor gene located on chromosome 13 (locus 13q14). The protein encoded by this gene normally blocks cell cycle progression out of the G1 phase and regulates differentiation. According to Knudson's classical "two-hit" hypothesis, two mutational events affecting the RB1 gene are required for tumor development. In the hereditary form, the first mutation is germline (inherited), and the second occurs as a somatic mutation in retinal cells. In the sporadic form, both mutations occur somatically within a single retinal cell. Today, this process is viewed as multifactorial, requiring the involvement of other genetic alterations.
Correction on terminology: The prompt's opening heading mentions nephroblastoma (Wilms tumor), while the text details neuroblastoma and retinoblastoma. Wilms tumor features a triphasic histology (blastemal, epithelial, and stromal elements).
Morphology and Spread Patterns of Retinoblastoma
The tumor originates in the retina, appearing macroscopically as a pinkish-white mass with areas of necrosis and calcification.
Microscopically, the tissue consists of small, round cells with scant cytoplasm and hyperchromatic nuclei, capable of forming ribbon-like structures. In more differentiated tumors, "true rosettes" (Flexner-Wintersteiner rosettes) are formed—palisading columnar or cuboidal cells arranged around a central lumen.
Invasive Growth Dynamics:
- Growth within the retina.
- Destruction of the internal limiting membrane.
- Invasion into the vitreous body and choroid.
- Filling the posterior chamber and extension through the globe wall.
- Destruction of orbital bone structures.
- Extension into the cranial cavity along the optic nerve.