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NBME 22 Answers

nbme22/Block 4/Question#39

A 5-year-old boy is brought to the physician ...

Retinal cells

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The physician said the boy is unlikely to develop any other neoplasms, so he doesn't have the inherited Rb mutation.

In this case, he has the sporadic retinoblastoma. Sporadic retinoblastoma requires two somatic mutations of Rb in the same retinal cell.

Just as a side note: Inherited retinoblastomas tend to be bilateral. Sporadic are unilateral.

carls14  aren't retinal cells a type of somatic cell? Why not is the mutation not considered in the somatic cell of the child? +  
omerta  Although this mutation would be considered somatic, I believe the question is just asking you to be specific as to which cells. If you answered "somatic cells of the child," that's quite broad and could apply to almost anything. +3  
kernicterusthefrog  I had the same struggle and thought process. +  
eacv  There is a Uworld qx that explain this in detail> ID: 863 +1