Metachronous or synchronous primary lung cancer in the era of computed tomography surveillance

OBJECTIVES: The purpose of this study was to determine the frequency, characteristics, and survival of second primary lung cancer initially identified as an indeterminate lesion on the original computed tomography scan and then diagnosed during the surveillance period in a prospective study. METHODS: A prospective database of 271 patients enrolled in a surveillance study was updated. Indeterminate lesions present on the original computed tomography at the time of initial primary lung cancer diagnosis that subsequently grew and were diagnosed as cancer were termed "synchronous primary lung cancer." Lesions that were not present on the original computed tomography scan and subsequently diagnosed on surveillance were termed "metachronous primary lung cancer." RESULTS: Thirty patients (11.1%) developed 37 second primary lung cancers over a median surveillance period of 84.7 (range, 15.9-147.6) months. Of these, 15 of 37 (40.5%) were identified as synchronous primary lung cancer, and 22 of 37 (59.5%) were identified as metachronous primary lung cancer. At first identification, ground-glass lesions were identified in 9 of 15 (60%) synchronous primary lung cancers compared with only 5 of 22 (22.7%) of metachronous primary lung cancers (P = .034). Compared with metachronous primary lung cancer, from first identification to diagnosis, synchronous primary lung cancer developed over a longer interval (33.6 vs 7.2 months, P = .001) and had a slower growth rate (0.17 vs 0.45 mm/month, P = .027). The 5-year overall survival from second lung cancer was 73.0%. No significant differences were observed between the synchronous primary lung cancer and metachronous primary lung cancer cohorts in overall survival from initial primary lung cancer (P = .583) or from second lung cancer (P = .966). CONCLUSIONS: Computed tomography surveillance identifies 2 types of curable second lung cancers leading to excellent overall survival.