“…12,18,19 The majority of second primary tumors are squamous cell carcinomas, with adenocarcinoma accounting for less than 10% in most series. 4,10 Thus, most commonly, the synchronous or metachronous tumors are of the same histologic type (squamous cell carcinoma), 20 but it is also reported possible to simultaneously have tumors of a different histologic feature. [21][22][23][24][25][26][27][28][29] Confusion persists whether an isolated lung lesion that is diagnosed is best considered a second primary or a secondary metastasis.…”