ACE2 and skin basal cell carcinoma: As ACE2 also serves as a biomarker of EMT and metastasis (15, 41), these data hinted that the upregulation of ACE2 by M protein-induced aggresstive BCC might facilitate the infection of SARS-CoV-2 and metastasis in non-aggressive BCC; suggesting that, in the heterogenous mixture of cells inside tumors, SARS-CoV-2-infected aggressive BCC may affect non-aggressive BCC through secretome and cytokine storm and promote a poor general outcome of tumor progression.