It may be easy to diagnose multicentric primary lung cancers in multiple lung lesions when their histological types are different. However, if they show the same histological type, it is often difficult to discriminate multiple primary lung cancers from intrapulmonary metastasis.
The differential diagnosis of intrapulmonary metastatic lung cancer (via bloodstream dissemination) verse primary lung cancer is also perplexing in clinical setting; however, tumors with consistent histology and N2 and N3 lymph nodes or multiple-organ metastasis are often diagnosed as intrapulmonary metastasis .
On the basis of the analyses of the overall survival among pathologically staged cases, nodules within the same lobe as the primary lesion are categorized by the International Union Against Cancer (UICC) as T4 and those located in the different lobe (whether it is ipsilateral or contralateral side) as M1. The International Association for the Study of Lung Cancer (IASLC) lung cancer-staging project recommended changes in the T classification to subclassify additional nodules in the same lobe as T3, nodules in the ipsilateral different lobe as T4, and those in a contralateral lobe as M1 . Their different biologic behaviors may, thus, be responsible for prognostic differences. Because some of the patients with intrapulmonary metastasis show poor prognosis, it is necessary to discriminate intrapulmonary metastasis from multiple primary lung cancers by exploring new practical techniques and markers.
The pathogenic mechanism of multiple primary lung cancer is still unclear, but several authors have reported the feasibility of clonal analyses between tumors to discriminate multiple primary lung cancers from intrapulmonary metastasis. A multiple-gene analysis to identify the clonality in a combination of multiple-gene mutations, such as a p53 gene mutation, K-ras mutation, and/or loss of heterozygosity, has been reported [19-24]. Mitsudomi analyzed the p53 gene mutation in 16 patients with multiple primary lung cancers . Among those patients, seven were not informative because of the absence of the p53 mutation in both tumors. Among nine patients who had at least one p53 mutation in their pair of tumors, six were suggested to be of different clonal origin and were diagnosed with multiple primary lung cancers. Matsuzoe reported that 7 of 20 patients who were clinically diagnosed to have intrapulmonary metastasis showed different p53 gene mutations between the two lesions, thus indicating these lesions to be multiple primary lung cancers . These reports indicate that the somatic mutations of the p53 gene may be a suitable biological factor to identify multiple primary lung cancers. Although there is a positive expression of the p53 due to a prolonged half-life time induced by a somatic mutation of the p53 gene, the concordance rate between p53 gene mutations and immunopositivity in NSCLC is reported to be 60% to 70% [27,28]. According to Ono’s study, the sum value of the differences in the expression ratio of four proteins (p53, p16, p27, and c-erbB2) was evaluated in immunohistochemically stained specimens among multiple primary lung cancers and intrapulmonary metastasis . Yoshimoto reported a case, diagnosed as double primaries, that is distinguished by EGFR gene mutation analysis .
Mercer et al.  found that detections of microsatellite alterations and deletion sites in tumor cell DNA could be used as diagnostic and prognostic markers for multiple cancers. In our previous study , the results demonstrated that molecular analysis of allelic variations at polymorphic microsatellite markers can be used to determine lineage relationships between multiple tumors, facilitating the discrimination of second primary cancer versus metastatic disease. With polymorphic microsatellite markers, the “unique trend” that represents metastasis cancers and the “contradictory trend” that represents primary multiple tumors are useful in the diagnosis between tumors found at the same time in the pulmonary even diagnosed with the histopathological evaluation.
In the first group, as the consequences showed of two patients in our study, alleles in patient 2 corresponding to microsatellite markers D2S1363 and D7S1824 were in the DNA from the first tumor but were reduced or not observed in the DNA from the second. In contrast, allele corresponding to D10S1239 was detected in the lung cancer (T2) that was not observed in the T1. Molecular analysis of these tumors identified discordant allelic variations involving three different microsatellite markers, arguing that these cancers arose independently. These mutually exclusive allelic losses strongly suggest that both of the neoplasms are not related. Thus, the lung cancer in this patient represents a second primary carcinoma rather than a solitary metastatic lesion derived from the other one. The characteristic of this “contradictory trend” is representative as our study before. However, in the case of patient 1, the two tumors share common allelic patterns for five microsatellite markers but show differing allelic patterns for only one microsatellite marker at D2S1363. The allele corresponding to the microsatellite marker D2S1363 was observed in T1 but was not detected in T2. The results strongly suggest that the T1 has given rise to T2 and suggest that the T1 metastasized to the T2. Given the histopathology for these neoplasms, a conclusion that a metastatic lesion derived from the other one was the same as ours. The “unique trend” is made with less confidence when the numbers of discordant changes are this few. Given that there is a concern about the effects of intra-tumor heterogeneity on this type of analysis, increased numbers of microsatellite markers (and observations of allelic variation) might be required to draw clear conclusions.
The next groups of tumors we studied were metachronous tumors with different histological types of the lung, and the result showed a “contradictory trend”. The paired tumors in case 3 appeared to be typical of the three patients. The observed allelic variation at D7S1824 suggests that T2 could be derived from T1, consistent with metastatic disease. However, the allelic variations of D2S1363, D6S1056, and D10S1239 were noted in T2 but not observed in T1; which means that T1 could be also derived from T2, so that the result contradicts the possible lineage relationship of metastatic disease.
Among the third group including seven intrapulmonary metastasis lung tumors diagnosed by pathology, the results of cases 6, 7, 8, 9, 10, and 12 present typical “unique trend” and it suggests that all the patients represent the real intrapulmonary metastasis lung tumors. However, the controversial consequences happened in patient 11. As the result showed before, patient 6 provided a clear example of a patient with two unrelated tumors, where the consequence suggests a “contradictory trend”. In this case, microsatellite markers D6S1056, D15S822, and D22S689 were observed in T2 but were not detected in T1. At the same time, alleles corresponding to microsatellite marker D10S1239 was observed in T1 but was not detected in T2.