Keywords: PET, positron emission tomography; PI3K, phosphatidylinositol-3 kinase; SCC, squamous cell carcinoma; SOTR, solid organ transplant recipient; calcineurin inhibitor; mTOR, mammalian target of rapamycin; mammalian target of rapamycin inhibitor; rapamycin; sirolimus; tacrolimus; undifferentiated carcinoma.