BACKGROUND: Controversies remain as to the differential diagnosis between multiple primary lung cancer (MPLC) and intrapulmonary metastasis (IM) in lung cancers. We have investigated the clinical criteria for MPLC and here propose a set of new and simple criteria from the stand point of prognosis. METHODS: A retrospective study was conducted on 588 consecutive patients with resected lung cancer of clinical Stage IA between 2009 and 2012. Multiple lung cancers (MLCs) were observed in 103 (17.5%) of the 588 patients. All main and other tumors were divided into solid tumor (ST) and non-solid tumor (non-ST). We defined Group A as MLCs having at least one non-ST and Group B as all tumors being ST. Cox's proportional hazard model was used for the multivariate analyses to investigate the preoperative prognostic factors. We divided the MLCs into MPLC and IM based on the preoperative prognostic factors, and survival was estimated by the Kaplan-Meier method. RESULTS: A multivariate analysis with Cox's proportional hazards model revealed that Group A independently predicted good overall survival (HR = 0.165, 95% CI: 0.041-0.672).Differences in the 3- and 5-year overall survivals between Groups A and B were statistically significant (96.3%/92.2% vs. 70.0%/60.0%, Pvalue = 0.0002). CONCLUSIONS: We suggest that Group A, defined as the presence of at least one tumor with a ground glass opacity component and clinical N0, should be excluded from the conventional concept of multiple lung cancers based on the criteria of Martini and Melamed as it has a very good prognosis. This group would be considered to be radiological MPLC.
BACKGROUND: Controversies remain as to the differential diagnosis between multiple primary lung cancer (MPLC) and intrapulmonary metastasis (IM) in lung cancers. We have investigated the clinical criteria for MPLC and here propose a set of new and simple criteria from the stand point of prognosis. METHODS: A retrospective study was conducted on 588 consecutive patients with resected lung cancer of clinical Stage IA between 2009 and 2012. Multiple lung cancers (MLCs) were observed in 103 (17.5%) of the 588 patients. All main and other tumors were divided into solid tumor (ST) and non-solid tumor (non-ST). We defined Group A as MLCs having at least one non-ST and Group B as all tumors being ST. Cox's proportional hazard model was used for the multivariate analyses to investigate the preoperative prognostic factors. We divided the MLCs into MPLC and IM based on the preoperative prognostic factors, and survival was estimated by the Kaplan-Meier method. RESULTS: A multivariate analysis with Cox's proportional hazards model revealed that Group A independently predicted good overall survival (HR = 0.165, 95% CI: 0.041-0.672).Differences in the 3- and 5-year overall survivals between Groups A and B were statistically significant (96.3%/92.2% vs. 70.0%/60.0%, Pvalue = 0.0002). CONCLUSIONS: We suggest that Group A, defined as the presence of at least one tumor with a ground glass opacity component and clinical N0, should be excluded from the conventional concept of multiple lung cancers based on the criteria of Martini and Melamed as it has a very good prognosis. This group would be considered to be radiological MPLC.