For patients with resectable lung cancer, anatomic resection alongside mediastinal lymph node dissection is pivotal in removing all tumor tissue visible on imaging from the patient's body. Despite these efforts, early relapse remains a significant issue. Literature review shows that the early relapse rate varies between 8 to 10%, potentially due to undetectable occult metastasis by imaging modalities, suggesting the presence of minimal residual disease or tumor cells evading the primary site. Limitations in imaging, such as the slice thickness in computed tomography (CT) scans, which range from 0.375 to 0.5 centimeters, can render tumors smaller than the slice thickness invisible. Similarly, tumors smaller than 0.5 cm may not accumulate sufficient F18-Deoxyglucose to be detectable in positron emission tomography (PET) scans. Additionally, tumor cells may migrate to extrapulmonary sites via lymphatic drainage or circulation.

Survival studies have predominantly focused on the pathologic TNM stage, which aggregates different disease presentations with similar survival outcomes. However, the heterogeneity inherent in pathology may help in identifying patients prone to relapse. From a tumor biology perspective, tumor cells may detach from surrounding tissues, becoming more invasive and entering the bloodstream. Circulating tumor cells (CTCs) have been recognized early in cancer stages and are correlated with treatment response, tumor genetic alterations, and survival. Research has combined CT tumor size and CTCs in a malignancy prediction model for suspicious pulmonary lesions, highlighting that CTCs can rebound in patients experiencing early relapse, indicating occult metastases or minimal residual disease.

Systemic adjuvant therapy is considered the best approach to minimize disease relapse in resectable lung cancer patients. Although many studies have sought to identify patients at risk of relapse to improve survival, the presence of intrapulmonary (N1) or mediastinal (N2) lymph node invasion significantly affects survival in non-small cell lung cancer patients. Even tumors smaller than 1 cm carry a risk of lymph node metastases, with respective risks for cT1a, cT1b, and cT1c tumors reported as 3.8%, 16.3%, and 19.6%. Therefore, patients with tumors larger than 1 cm are recommended adjuvant therapy due to the high risk of lymph node involvement. Adjuvant chemotherapy is advised for patients with stages 1b to 3a, showing a 5.4% survival benefit by the fifth postoperative year, although this benefit diminishes in subsequent years. This could be due to adjuvant therapy being administered based on the pathologic stage rather than the likelihood of relapse. Tumor heterogeneity might also influence the response to different therapeutic regimens. Molecular profiling of tumors has identified mutations predicting responses to targeted therapies and elucidated drug resistance mechanisms, offering more precise treatments and improving survival. Targeted and immune therapies have shown improved survival in specific tumor subgroups.

This study aims to utilize trends in CTC variations as a screening tool to identify patients at risk of relapse and prescribe adjuvant therapy to evaluate the therapeutic efficacy and survival impact of CTCs.