Twelve weeks following the intratracheal administration of virus-containing solutions, both KPCRISPR and KPGEMM mice developed tumors; tracheal and oral examination of the infected mice showed no signs of off-target tumor formation; and there were no appreciable differences between KPGEMM and KPCRISPR in terms of tumor cell proliferation, as indicated by the percentage of proliferating cell nuclear antigen (PCNA)-positive cells within the tumors, or tumor burden, as assessed by hematoxylin and eosin (HE) staining. The gene discussed is PCNA; the disease is neoplasm.