Differential Diagnosis of Multiple Primary Lung Cancers and Intra-Lung Metastasis by Multiple Gene Detection

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Differential Diagnosis of Multiple Primary Lung Cancers and Intra-Lung Metastasis of Lung Cancer by Multiple Gene Detection

The distinction between multiple primary lung cancers (MPLC) and intrapulmonary metastases (IM) holds significant clinical implications for tumor staging and treatment strategies. With advancements in diagnostic technologies and increased health awareness leading to early detection of multifocal lung cancer, the need for accurate differentiation has become paramount. Traditional diagnostic criteria, such as those established by Martini and Melamed in 1975 and later revised by the American College of Chest Physicians (ACCP) in 2003, rely on histological and clinical features. However, these criteria may not fully account for the molecular heterogeneity of tumors. This study explores the utility of multi-gene detection in differentiating MPLC from IM, leveraging clonal origin discrepancies to refine diagnostic accuracy.

Clinical and Molecular Context

MPLC refers to the presence of distinct primary tumors within the lungs, whereas IM arises from the spread of a single primary tumor. Accurate differentiation influences staging, prognosis, and therapeutic decisions, such as the extent of surgical resection or eligibility for targeted therapies. The ACCP criteria emphasize histological discordance, anatomical distribution, and the absence of systemic metastases to classify MPLC. However, overlapping features between MPLC and IM often complicate diagnosis, necessitating molecular insights to resolve ambiguity.

Methodology

The study analyzed 50 patients diagnosed with multifocal lung cancer at the First Affiliated Hospital of Nanjing Medical University between 2014 and 2017. Formalin-fixed paraffin-embedded (FFPE) tissue blocks were examined, with tumor cell content ≥30% required for inclusion. DNA and RNA were extracted using specialized kits (AmoyDx-FFPE DNA/RNA extraction kits) and screened for mutations in 11 driver genes: EGFR, ALK, ROS1, MET, KRAS, RET, HER-2, BRAF, NRAS, and PIK3CA. Mutation analysis employed ADx-5 and ADx-MET detection kits, designed to identify single nucleotide variants, insertions, deletions, and fusion events.

Clinical data, including age, smoking history, histology, lesion distribution, and lymphatic metastasis, were correlated with molecular profiles. Follow-up data on progression-free survival (PFS), treatment response, and recurrence were collected, with 11 patients lost to follow-up. Statistical analyses compared mutation concordance rates between MPLC and IM cohorts using Fisher’s exact test. Survival outcomes were evaluated via Kaplan-Meier curves and Cox regression models.

Key Findings

Mutation Concordance and Discordance

Among 50 cases, 33 (66%) exhibited genetic results consistent with ACCP classifications, while 10 (20%) showed discrepancies. Mutation consistency rates were significantly higher in IM (64%, 7/11) than in MPLC (19%, 6/31) (P = 0.019), as illustrated in a mutation heat map integrating histology, lesion stage, smoking status, and survival (Figure 1). For example, IM cases frequently shared driver mutations such as EGFR exon 19 deletions, whereas MPLC displayed heterogeneous profiles, including KRAS G12V and PIK3CA E545K in separate lesions.

Survival Analysis

Kaplan-Meier analysis revealed superior PFS in patients with detectable mutations (P = 0.001), no lymphatic metastasis (P = 0.001), ACCP-classified MPLC (P = 0.038), and discordant mutational profiles (P = 0.002). Cox regression confirmed these trends:

  • Mutation carriers had a median PFS of 1579 days (95% CI: 1440–1718) versus 848 days (95% CI: 444–1253) in non-carriers (HR = 0.123; P = 0.005).
  • Patients without lymphatic metastasis demonstrated a median PFS of 1610 days (95% CI: 1483–1737) compared to 1014 days (95% CI: 597–1430) in those with metastasis (HR = 0.132; P = 0.006).
  • ACCP-classified MPLC cases had a median PFS of 1594 days (95% CI: 1450–1738) versus 1233 days (95% CI: 895–1571) for IM (HR = 0.246; P = 0.045).

Diagnostic Discrepancies

Ten cases exhibited discordance between ACCP and molecular criteria. Six ACCP-classified MPLC cases showed identical mutations (e.g., concurrent EGFR L858R in two lesions), challenging the assumption of clonal independence. Conversely, two ACCP-classified IM cases harbored divergent mutations (e.g., NRAS Q61K in one lesion and wild-type in another), suggesting potential misclassification. Notably, one patient with three lesions had two metastatic foci sharing a HER-2 mutation and a third wild-type lesion, underscoring the complexity of multifocal disease.

Discussion

Molecular Insights into Clonality

Identical mutations in separate lesions typically indicate a common clonal origin, favoring IM. However, prevalent driver mutations like EGFR exon 19 deletions (30–50% in Asian lung adenocarcinomas) may coincidentally arise in independent primaries, necessitating integration of histopathological and clinical data. For example, a patient with two EGFR L858R-mutant lesions but distinct histologies (adenocarcinoma vs. squamous cell carcinoma) was classified as MPLC despite molecular overlap, highlighting the limitations of relying solely on mutation profiles.

Clinical Implications of Mutation Heterogeneity

The study identifies scenarios where multi-gene detection adds diagnostic value:

  1. Discordant Histology with Concordant Mutations: Three cases displayed histologically distinct tumors sharing identical mutations (e.g., ALK fusion in adenocarcinoma and squamous cell carcinoma), suggesting stem cell differentiation rather than separate primaries.
  2. Wild-Type vs. Mutant Lesions: A subset of IM cases featured mutations in one lesion but not others, possibly due to subclonal populations below detection thresholds in the primary tumor.
  3. Rare Mutations as Metastatic Markers: A patient with dual HER-2 mutations (1–2% prevalence in Asian cohorts) was reclassified as IM, as the low population frequency makes independent acquisition unlikely.

Limitations and Future Directions

The study’s retrospective design and small sample size limit generalizability. Additionally, tumor heterogeneity and technical limitations in detecting low-frequency variants may affect accuracy. Future studies incorporating whole-exome sequencing or circulating tumor DNA analysis could enhance resolution.

Conclusion

Multi-gene detection complements traditional criteria in differentiating MPLC and IM, particularly in cases with ambiguous histopathology. Mutation concordance supports IM, while discordance favors MPLC, though prevalent mutations require cautious interpretation. Integration of molecular, histological, and clinical data optimizes diagnostic precision, guiding personalized treatment and improving prognostic assessments.

doi.org/10.1097/CM9.0000000000001739

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