A 4-year-old boy presents with morning headache, vomiting, and truncal ataxia. MRI shows a midline cerebellar mass with hydrocephalus. Histology shows small round blue cells with Homer Wright rosettes. Molecular testing shows CTNNB1 mutation and monosomy 6. Which molecular subgroup does this tumor belong to, and what is its prognosis?

• A Group 4, worst prognosis
• B SHH-activated, intermediate prognosis
• C Group 3, worst prognosis
• D WNT-activated, most favorable prognosis ✓

Explanation

CTNNB1 (beta-catenin) mutation defines the WNT-activated medulloblastoma subgroup, which carries the best survival, exceeding 90 to 95 percent with therapy. These tumors are classically classic histology, occur in older children, and are often midline cerebellar. SHH-activated tumors correlate with nodular/desmoplastic histology and TP53 mutations in the adult form. Group 3 carries the worst prognosis and is associated with MYC amplification and metastasis. Group 4 is the most common but has intermediate outcome.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.