INTRODUCTION Differentiating between multiple primary lung cancer (MPLC) and intrapulmonary metastasis (IPM) is critical for developing a therapeutic strategy to treat multiple lung cancers with multiple pulmonary sites of involvement. METHODS We retrospectively included 252 lesions (126 pairs) from 126 patients with surgically resected multiple lung adenocarcinomas. Each pair was classified as MPLC or IPM based on histopathologic findings as the reference standard. A novel algorithm was established with four sequential decision steps based on the combination of computed tomography (CT) lesion types (Step 1), CT lesion morphology (Step 2), difference of maximal standardized uptake values on positron-emission tomography/CT (Step 3), and presence of N2/3 lymph node metastasis or distant metastasis (Step 4). The diagnostic accuracy of the algorithm was analyzed. Performances of eleven observers were assessed without and with knowledge of algorithm. RESULTS Among 126 pairs, 90 (71.4%) were classified as MPLCs and 36 (28.6%) as IPMs. On applying the diagnostic algorithm, the overall accuracy for diagnosis of IPM among conclusive cases up to step 4 was 88.9%, and 65 and 44 pairs were correctly diagnosed based on Step 1 and Step 2, respectively. Specificity and positive predictive value for diagnosis of IPM increased significantly in all observers compared with reading rounds without the algorithm. CONCLUSIONS Application of the algorithm based on comprehensive information on clinical and imaging variables can allow differentiation between MPLCs and IPMs. When both of two suspected malignant lesions appear as solid predominant lesions without spiculation nor air-bronchogram on CT, IPM should be considered.

中文翻译：

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一种区分多原发肺癌和多发肺受累多发肺癌肺内转移的新算法

引言 区分多原发肺癌 (MPLC) 和肺内转移癌 (IPM) 对于制定治疗多发性肺癌的治疗策略至关重要。方法 我们回顾性纳入了 126 名手术切除的多发性肺腺癌患者的 252 个病灶（126 对）。根据作为参考标准的组织病理学发现，每对被分类为 MPLC 或 IPM。基于计算机断层扫描 (CT) 病变类型（步骤 1）、CT 病变形态（步骤 2）、正电子发射断层扫描/CT 上最大标准化摄取值的差异（步骤3），存在N2/3淋巴结转移或远处转移（步骤4）。分析了算法的诊断准确性。在不了解和了解算法的情况下评估了 11 位观察者的表现。结果 在 126 对中，90 对 (71.4%) 被归类为 MPLC，36 (28.6%) 被归类为 IPM。在应用诊断算法时，到步骤 4 的结论性病例中 IPM 诊断的总体准确率为 88.9%，根据步骤 1 和步骤 2 分别正确诊断了 65 和 44 对。与没有算法的阅读轮次相比，所有观察者对 IPM 诊断的特异性和阳性预测值都显着增加。结论 应用基于临床和影像变量综合信息的算法可以区分 MPLC 和 IPM。