MYC and cancer: Interestingly, this inherent adaptability is evident even within subtypes of the same cancer, as analyses of small cell lung cancers has revealed a subset dependent on Myc-driven inosine monophosphate dehydrogenase (IMPDH) activity specifically for ribosomal RNA (rRNA) synthesis over mRNA synthesis, suggesting multiple avenues of metabolic adaptation as it pertains to nucleotide metabolism beyond the need for synthesis of genomic DNA (57).