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.

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.