Utility of consolidation-to-tumor ratio and solid component size for risk stratification of occult lymph node metastasis in early-stage lung adenocarcinoma: a retrospective cohort study

The optimal cutoff values for consolidation-to-tumor ratio (CTR) and solid component size in relation to nodal metastasis vary among study populations, and their combined use for preoperative occult lymph node metastasis (OLNM) risk stratification has not been well established. This study evaluated the associations of CTR and solid component size with OLNM and examined a four-group classification combining these radiological measures in early-stage lung adenocarcinoma. We retrospectively reviewed patients with cTis–T2aN0M0 lung adenocarcinoma who underwent anatomical pulmonary resection with lymph node dissection at our institution between 2013 and 2022. Receiver operating characteristic curve analyses were performed to identify candidate cutoff values for CTR and solid component size. Patients were classified as Group 1 (CTR < 0.8, solid component size < 2.0 cm), Group 2 (CTR ≥ 0.8, solid component size < 2.0 cm), Group 3 (CTR < 0.8, solid component size ≥ 2.0 cm), or Group 4 (CTR ≥ 0.8, solid component size ≥ 2.0 cm). Associations between the four-group classification and OLNM were evaluated using Firth’s penalized logistic regression with adjustment for age, serum carcinoembryonic antigen level, and the presence or absence of mediastinal lymph node dissection. Among 435 patients, OLNM was identified in 39 (9.0%), including 21 with pN1 and 18 with pN2 disease. The areas under the receiver operating characteristic curves were 0.784 (95% confidence interval [CI], 0.735–0.832) for CTR and 0.746 (95% CI, 0.680–0.811) for solid component size. The observed OLNM frequencies (exact 95% CIs) were 0/181 (0.0%; 0.0–2.0%), 9/86 (10.5%; 4.9–18.9%), 2/34 (5.9%; 0.7–19.7%), and 28/134 (20.9%; 14.4–28.8%) in Groups 1–4, respectively. The four-group classification was associated with OLNM after adjustment for age, serum carcinoembryonic antigen level, and mediastinal lymph node dissection (penalized likelihood-ratio χ² = 33.53, 3 degrees of freedom; P < 0.001). A sensitivity analysis restricted to patients who underwent mediastinal lymph node dissection yielded consistent findings. Combining CTR and solid component size stratified patients into groups with different observed frequencies of OLNM. Although no OLNM was observed among patients with both CTR < 0.8 and solid component size < 2.0 cm, this finding should not be interpreted as complete absence of risk. External validation is required before clinical application.