Next-generation sequencing facilitates differentiating between multiple primary lung cancer and intrapulmonary metastasis: a case series

BACKGROUND: In lung cancer management, differential diagnosis between multiple primary lung cancer (MPLC) and intrapulmonary metastasis (IMP) is a critical point that is of direct therapeutic and clinical importance. However, this process often suffers from absence of a gold standard, resulting in equivocal cases. Herein, we present a series of three cases, in which genomic alteration patterns revealed by next-generation sequencing (NGS) facilitated the differential diagnosis between MPLC and IMP. CASE PRESENTATION: Case 1 was a 57-year-old female with two separate lesions in the upper lobe and the lower lobe of left lung, which were both histopathologically determined as T2aN0M0 adenocarcinomas. NGS identified an EGFR L858R in one lesion and an EGFR 20 exon insertion in the other one, suggestive of double primary malignancies. The patient underwent wedge resections and received an adjuvant treatment of icotinib and chemotherapy. She had a disease-free survival (DFS) of 19 months and counting. Case 2 was a 55-year-old female with multiple small lesions in both lungs. Histopathological examinations of resected lesions from right upper lobe revealed three subtypes: atypical adenomatous hyperplasia of alveolar epithelium, adenocarcinomas in situ and minimally invasive adenocarcinoma. NGS identified two different BRAF driver mutations G466E and V600_K601delinsE in two lesions of adenocarcinoma in situ, and a BRAF K601E in a lesion of minimally invasive adenocarcinoma. Case 3, a 68-year-old male, had the right upper lobe lesion histophathologically classified as a stage T3NxM0 mixed adenoneuroendocrine carcinoma and the left upper lobe lesion as a stage T1aN0M0 adenocarcinoma. NGS performed with different loci of surgical tissues revealed a rare sensitizing EGFR mutation G719A shared by the right upper lobe lesion and lymph node, and two EGFR mutations L861Q and G719S in left upper lobe lesion. The patient received icotinib treatment postoperatively and achieved a stable disease with a progression-free survival of 5 months. CONCLUSION: Our cases provide evidence for utility of NGS in facilitating diagnosis and treatment decisions. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13000-021-01083-6.