Criteria for the diagnosis of synchronous primary lung carcinomas:
(1) grossly separate and distinct lesions
(2) one of the following:
(2a) histologically distinct
(2b) histologically similar AND all of the following:
(2b1) not in the same lung segment
(2b2) no lymphatic spread in vessels common to both tumors
(2b3) no extrapulmonary metastases at the time of the diagnosis
(2b4) arising from carcinoma in situ
Differential diagnosis for synchronous primary lung carcinomas:
(1) metastasis from lung primary
(2) metastases from an extrapulmonary carcinoma
(3) metachronous primary carcinomas (primary carcinomas arising at different times)
Failures in criteria with respect to recognition of metastatic carcinoma:
(1) variation in histologic appearance of a poorly differentiated carcinoma
(2) failure to detect lymphatic invasion
(3) failure to detect extrapulmonary metastasis or extrapulmonary primary
(4) absence of carcinoma in situ
where:
• Carcinoma in situ might be seen with a squamous cell carcinoma of the lung but not with other cell types.
