Tumorudviklingen blev forudgået af pneumocytproliferation i lungen, som ikke observeredes hos rotter, hunde eller aber, hvilket tyder på at nøglehændelsen i udviklingen af lungetumorer hos mus sandsynligvis er artsspecifik.
Tumour development was preceded by pneumocyte proliferation in the lung which was not observed in rats, dogs, or monkeys, indicating that a key event in lung tumour development observed in mice likely was species-specific.