DNA ploidy analysis of squamous cell head and neck cancer to identify distant metastasis from second primary

We conducted an investigation by flow cytometry to determine whether lung cancer in eight patients with oral cancer represented a metastasis or a second primary. One patient had the same aneuploid cell population at both sites which indicated the lung lesion to be a metastasis. Two patients had a diploid lesion at both sites. In these patients, a second primary could not be distinguished from a distant metastasis because (notwithstanding both lesions being diploid) the tumors may have a different DNA content but at a level too low for flow cytometric detection. Five cases had differing DNA indices, which could represent a second primary as well as the emergence of a new clone during tumor progression and metastasis. It appears that DNA flow cytometry can identify tumors that are the same if both have the same aneuploid pattern, but it cannot prove that they are different.