Peripheral Vascular Disease as a Clinical Trigger for Opportunistic Lung Cancer Screening Referral: An Implementation Study

Overview

The study aims to determine whether patients with peripheral vascular disease who attend the vascular clinics are eligible for lung cancer screening. This is because long-term cigarette smoking exposure is associated with peripheral vascular disease, and smoking is again the main risk factor for lung cancer. These clinical encounters provide a potential opportunity to identify individuals who may qualify for lung cancer screening but are not routinely assessed for screening eligibility. Integrating systematic screening eligibility assessment within vascular clinics could therefore represent an effective strategy for identifying high-risk individuals and improving referral for lung cancer screening. Additionally, peripheral arterial disease is commonly diagnosed using the ankle-brachial index (ABI), a non-invasive measure that compares systolic blood pressure between the ankle and brachial arteries. An ABI value below 0.90 is widely recognised as diagnostic of peripheral arterial disease and reflects the presence of systemic atherosclerosis. ABI has been increasingly recognized as a marker of cumulative exposure to cardiovascular risk factors, particularly long-term tobacco smoking. Tobacco smoking contributes to endothelial dysfunction, chronic inflammation, and atherosclerotic plaque formation, mechanisms that are also implicated in lung carcinogenesis. Because both lung cancer and peripheral vascular disease share major risk factors, ABI may serve as a clinical proxy indicator of cumulative smoking-related vascular damage. Individuals with lower ABI values may therefore represent a subgroup with higher cumulative tobacco exposure and potentially elevated lung cancer risk. Evaluating the association between ABI severity categories and lung cancer diagnosis may provide insights into whether vascular disease severity could help identify individuals who may benefit from targeted screening interventions. If an association is observed, ABI could potentially be used as a simple, routinely measured clinical indicator to prompt lung cancer screening assessment in vascular care settings. Therefore, this study will determine the proportion of the vascular disease patients who fall under the high-risk group for lung cancer screening and refer them to low-dose CT scan and follow-up them for the results and the adherence.

Primary Objective: To estimate the proportion of patients with peripheral vascular disease eligible for and referred to lung cancer screening in a tertiary healthcare setting Secondary Objectives: * To assess the potential for expanded eligibility criteria for screening, by the inclusion of peripheral vascular disease as an additional risk stratification measure * To quantify the distribution of smoking exposure(pack-years), ABI values, and other lung cancer risk factors in patients with peripheral vascular disease. * To assess the association between ABI categories and the low-dose CT scan findings. * To evaluate the feasibility of the risk-based lung cancer screening from vascular clinics in the tertiary care set-up using implementation science frameworks Study design: The investigators will conduct a prospective study among patients diagnosed with peripheral vascular disease at a tertiary care hospital. The investigators will assess lung cancer screening eligibility among these patients and the feasibility of implementing lung cancer screening for patients referred from the vascular clinics in the tertiary healthcare setting using RE-AIM implementation science framework. Study population: All individuals, aged 40 and above, diagnosed with a peripheral vascular disease in the surgical, medical and cardio-vascular OPDs in the tertiary care hospital. Although current lung cancer screening recommendations generally target adults aged 50 years and older with substantial smoking exposure(20 pack-years), this study includes participants aged 40 years and above due to the presence of peripheral vascular disease (PVD), a condition strongly associated with long-term tobacco exposure and systemic atherosclerosis. Peripheral vascular disease often manifests earlier than other smoking-related malignancies and may serve as a clinical marker of cumulative vascular and inflammatory damage related to chronic smoking. Furthermore, the ankle-brachial index (ABI), an objective measure of peripheral arterial disease severity, reflects the burden of systemic atherosclerosis and long-term exposure to shared risk factors such as tobacco use, ageing, and chronic inflammation. Patients presenting with abnormal ABI values may therefore represent a risk-enriched subgroup in which earlier evaluation for lung cancer risk may be justified. Including individuals aged 40 years and above allows this study to explore whether PVD and ABI abnormalities can function as additional clinical indicators to identify high-risk individuals who may otherwise fall outside conventional age-based screening thresholds. Additionally, the investigators will screen patients with pack-years 15 and above(and not quit in last 15 years), as they are already peripheral vascular disease patients and have considerable vascular damage. Exclusion criteria: * Prior diagnosis of lung cancer established/on work-up * Patients with no smoking history * Patients not eligible for low-dose CT scan Study period: The study period is June 2026- January 2027, with 6 months for recruitment of an adequate number of sample size with additional months for follow up of the set of individuals who were referred for low-dose CT scan lung cancer screening Study Procedure: The study will include all individuals diagnosed with a peripheral vascular disease, with age more than 40 years, in the surgical, cardio-vascular and medical outpatient departments in the hospital. The investigators will collect data on the socio-demographic profile and lung cancer-related history and co-morbidity details from these patients. The investigators will assess the eligibility for lung cancer screening in these individuals by calculating the smoking history (pack years). Further, the ankle-brachial index in these patients will be evaluated, as per the standard specifications. Patients who meet the criteria for lung cancer screening will be referred for low-dose computed tomography screening. The lung cancer screening criteria, as prescribed by USPSTF: Individuals aged 50 to 80 years who have more than 20 pack-years of smoking history and currently smoke or have quit within the past 15 years will be the standard criteria for screening in this study. For this study purpose, since PVD is included as an additional condition, the investigators will screen participants who are more than 40 years old and those with pack years of 15 and above, and not quit in last 15 years in addition to the standard criteria, as a disease due to this major risk-factor is already established in them. This would be an expanded eligibility criteria for screening and forms the exploratory group in the study. Patients who do not report to the LDCT appointment will be contacted by the research assistant up to 2 times with rescheduled dates. Reason for non-attendance will be noted. After the LDCT, those with lung lesions will be referred to the regional cancer centre for further management and follow-up to confirm the diagnosis. Study setting: The study will be conducted in the tertiary care district headquarters hospital. Out-patient departments which cater to peripheral vascular disease patients: Surgical, Medical and cardio-vascular departments will be involved for patient recruitment. However, patients will be assessed by the investigator from the surgical department, and the radiology department will offer the LDCT screening services for those referred from the surgical department, as part of the study. Sample size: The sample size has been calculated using eligibility for lung cancer screening as the outcome of interest. Assuming that 30% of the patients with a peripheral vascular disease will be eligible for lung cancer screening, and 95 percent confidence interval, the sample size is 323 participants. Considering a 10% non-response rate, 355 participants with peripheral vascular disease have to be recruited and assessed. Outcomes: The primary outcomes of the study will measure the proportion of peripheral vascular disease patients, found eligible for lung cancer screening (as per standard screening recommendations - USPSTF) The secondary outcome indicators will measure the following: * Proportion of patients found additionally eligible for the expanded screening eligibility * Distribution and association of ABI with screening eligibility * Proportion of patients with peripheral vascular disease assessed for lung cancer screening eligibility (Reach) * Proportion of eligible patients referred for LDCT screening (Adoption) * Proportion of referred patients who complete LDCT screening (Uptake) * Proportion of screened participants with lung nodules or suspected malignancy (Detection Yield) - for standard and expanded LCS