This multicenter prospective cohort study will enroll adults who have undergone resection of a primary pulmonary nodule and have residual multiple pulmonary nodules or require routine postoperative pulmonary nodule follow-up. During clinically indicated follow-up visits, a small amount of peripheral venous blood will be collected at the same time as routine blood draws for research CyTOF immune phenotyping and viral imprinting-related serology. The study will not assign participants to treatment, change follow-up schedules, imaging, medication, surgery, or other clinical care. Research laboratory results will not be returned to participants or entered into medical records. The study will describe longitudinal peripheral immune-cell profiles and explore associations among T/B/NK cell phenotypes, T-cell differentiation and senescence/exhaustion markers, viral imprinting markers, and postoperative residual or new pulmonary nodule evolution.

The study is designed as a multicenter, prospective, non-randomized observational cohort. Eligible participants will be identified in thoracic surgery clinics, inpatient services, or routine postoperative follow-up programs at participating centers. After written informed consent, research blood samples of no more than 10 mL per time point will be collected together with routine clinical blood draws when available. No additional clinic visit, imaging examination, treatment, surgery, drug, device, vaccination, or other clinical intervention will be scheduled for research purposes. Peripheral blood will be analyzed using CyTOF mass cytometry to characterize major T-cell, B-cell, and NK-cell lineages, T-cell Naive/TCM/TEM/TEMRA differentiation, CD57-related senescence, activation markers, and immune checkpoint/exhaustion-related markers. Viral imprinting-related serology may include CMV IgG, EBV VCA-IgG, EBV EBNA-IgG, HPV L1-related antibodies, or other tests available within the approved institutional laboratory scope. Clinical and exposure data will be abstracted from routine records and study CRFs, including demographics, smoking and exposure history, relevant comorbidities, pulmonary nodule characteristics, pathology, imaging follow-up, and subsequent biopsy or surgery. Analyses will describe longitudinal immune phenotypes and evaluate exploratory associations between immune reserve, immune senescence, viral imprinting markers, and pulmonary nodule stability, enlargement, new nodule development, imaging risk upgrade, repeat biopsy, or repeat surgery. All research assay results are for group-level research only and will not be used to guide individual diagnosis, treatment, imaging interval, medication, or surgical decisions.

Inclusion Criteria:

Age 18 years or older, any sex. Primary pulmonary nodule has been surgically resected, with residual multiple pulmonary nodules or a need for pulmonary nodule-related routine postoperative follow-up.

Planned routine postoperative follow-up at a participating center and able to provide a research blood sample together with routine blood draw when clinically available.

Able to understand the study and willing to provide written informed consent before research blood sample collection.

Exclusion Criteria:

Investigator judges that the participant is unsuitable for additional small-volume blood collection, such as severe anemia, obvious coagulation abnormality, recent severe bleeding, or high risk of severe vasovagal reaction.

Acute severe infection, acute major organ dysfunction, or other condition that may substantially affect peripheral immune status and makes study participation unsuitable.

Current strong immunosuppressive therapy that may substantially affect peripheral immune status and cannot be adequately recorded or adjusted for in analysis.

Unable to complete informed consent or explicitly refuses use of research blood samples and related data for this study.

Any other condition that, in the investigator's judgment, makes participation inappropriate.

Adults who have undergone surgical resection of a primary pulmonary nodule and have residual multiple pulmonary nodules or require routine postoperative pulmonary nodule follow-up at participating centers. Participants will be identified from thoracic surgery clinics, inpatient services, and routine postoperative follow-up programs. Eligible participants will provide written informed consent and will be followed according to usual clinical care; research blood samples and study data will be collected at clinically scheduled visits when routine blood draws and follow-up data are available.