Introduction

Lung cancer remains the leading cause of cancer mortality in Canada, with nearly 30,000 new cases diagnosed annually and more deaths than any other malignancy [1,2]. Approximately half of all lung cancer cases in Canada are diagnosed at stage IV, when treatment options are most limited and survival is poor. Early-stage detection is critical, as five-year survival for stage I lung cancer is reported at 61%, compared with approximately 3% for stage IV disease [3].

Despite its public health importance, lung cancer continues to be diagnosed late in many populations [4]. Social determinants of health (SDOH), such as socioeconomic status (SES), continuity of primary care, immigration status, and geographic access to services, are increasingly recognized as factors influencing both stage at diagnosis and subsequent treatment patterns [5–7]. SES inequalities in lung cancer outcomes have been documented in multiple settings, with lower income and reduced health care access linked to more advanced disease and poorer survival [8]. Additionally, migrant populations comprise a significant proportion of Canada’s demographic profile, yet evidence is mixed on whether immigrant status independently influences stage at diagnosis or outcomes. Population studies in Ontario suggest that immigrant status may not be associated with a higher likelihood of late-stage diagnosis, but variability persists by sociodemographic context [9,10].

Although Canadians benefit from a universal healthcare system, social disparities influence access to care, treatment received, and cancer outcomes [11]. In this study, we use population-level health administrative databases to identify associations between SDOH influence lung cancer stage at diagnosis and subsequent treatment.

Methods

Results

We identified 130,825 patients diagnosed with lung cancer between January 2007 and December 2023. Of these, 106,867 (81.7%) had stage data available. Males comprised 50.6% (54,124 / 106,867) of the total cohort. The largest age group were those between 70–79 years (33.8%) with the remaining aged <50 years (2.9%), 60–69 years (30.0%), and ≥80 (20.2%). Stage distributions were as follows: Stage I 20,393 (19.1%); Stage II 7,826 (7.3%); Stage III 22,427 (21.0%); Stage IV 56,221 (52.6%). In the period 2020–2023 there were more Stage I and fewer Stage IV diagnoses than previous years. Table 1 illustrates the demographic factors associated with stage at diagnosis.

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Table 1. Demographic factors associated with clinical stage at presentation.

https://doi.org/10.1371/journal.pone.0354330.t001

Table 2 depicts the social determinants of health associated with stage at diagnosis. There were a greater number of patients not rostered with a family physician diagnosed with stage IV lung cancer (62.1%) compared with those fully rostered (51.5%) and those only virtually rostered (55.7%). Those deemed to be immigrants were more likely to be diagnosed as stage IV (55.6%) compared to non-immigrants (52.4%). New immigrants (those living in Canada ≤5 years before diagnosis) were more likely to be diagnosed as stage I (22.0% vs 19.0%) and less likely to be diagnosed as stage IV (49.7% vs 52.6%) compared to non-immigrants. There was a similar distribution of stage amongst the household income quintiles and neighbourhood income quintiles. Patients living within 50 km of a regional cancer centre were more likely to be diagnosed at stage IV compared to those living > 100 km from the nearest cancer centre (53.4% vs 49.8%). Patients living in the southwest region of the province were the least likely to be diagnosed at stage I (16.9%) whereas those in the central region of the province were the most likely to be diagnosed with stage IV disease (52.6%).

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Table 2. Social determinants of health associated with clinical stage at presentation.

https://doi.org/10.1371/journal.pone.0354330.t002

Table 3 demonstrates factors associated with a diagnosis of stage IV lung cancer using logistic regression. Females were significantly less likely to be diagnosed with stage IV disease (OR=0.85, p-value <0.001). The likelihood of a stage IV diagnosis significantly decreased with advancing age (e.g., OR=0.82, p-value <0.001 for >80 years compared to < 50 years), increasing household income (OR=0.92, p-value <0.001 for quintile 5 compared to quintile1), immigrant status (OR=0.77, p-value 0.001), and distance from the nearest cancer centre (OR=0.90, p-value <0.001 for >50km compared to <50km). Likelihood of stage IV diagnosis increased with frailty (OR=1.01, p-value 0.009), not being rostered with a family physician (OR=1.55, p-value<0.001 when compared with those fully rostered). The likelihood of a stage IV diagnosis significantly increased over time (OR=1.30 p-value<0.001 for years 2010–2014 compared to 2007–2009) but then levelled out in the later period of years 2020–2023 (OR=1.03, p-value 0.133). Those in the east and north were significantly less likely to receive a stage IV diagnosis compared to those in the Central region (OR=0.87 p-value <0.001, OR=0.88 p-value <0.001, respectively).

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Table 3. Regression analysis demonstrating likelihood of Stage IV diagnosis.

https://doi.org/10.1371/journal.pone.0354330.t003

Table 4 illustrates factors associated with receipt of surgery for lung cancer. 56.1% of stage I patients had surgery whereas 1.4% of patients with stage IV lung cancer underwent surgical resection. The likelihood of receiving surgery decreased as age increased (27.0% of those aged <50 compared to 7.3% of those aged ≥80 years). Increased comorbidity burden was associated with less likelihood of receiving surgery (25.4% for 0 comorbidities versus 5.0% for ≥5 comorbidities). Those not rostered with a family physician were less likely to receive surgery (9.3%) compared with fully rostered (18.8%) and virtually rostered (14.9%) patients. Immigrants, including recent immigrants, were more likely to receive surgery than non-immigrants (22.0% vs 17.5%). Increasing household income was associated with a reduced likelihood of receiving surgery, whereas increasing neighbourhood income was associated with an increased likelihood of receiving surgery. Those in the central region of the province were most likely to receive surgery (21.2%) whereas those in eastern region were the least likely (15.0%).

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Table 4. Factors associated with receipt of surgery.

https://doi.org/10.1371/journal.pone.0354330.t004

Discussion

In this population-level study of incident lung cancer cases in Ontario, we found strong and consistent associations between SDOH and stage at diagnosis, as well as subsequent receipt of surgical treatment. This present study is the first contemporary report that investigates the association between SDOH and stage of lung cancer at diagnosis in an unselected cohort of over 106,000 patients. Despite universal health insurance in Ontario, marked gradients in stage at presentation and access to potentially curative surgery persisted across socioeconomic, geographic, and primary care attachment factors. We have previously reported that immigrants, those fully rostered with a family physician, and those in the higher income quintiles were more likely to undergo surgical resection for stage I lung cancer [11]. This current study builds on that previous work and demonstrates social inequities in lung cancer stage at diagnosis.

Younger age was strongly associated with a likelihood of stage IV disease compared to all other age groups. This pattern is inconsistent with previous literature [14,15] that shows delayed diagnosis among older adults, potentially reflecting atypical symptom presentation and lower likelihood of referral for aggressive diagnostic workup. In our data, it is likely that older patients, who carry a higher comorbidity burden, have early-stage lung cancer identified during the diagnostic workup of other comorbid conditions. However, comorbidity burden was also independently associated with more advanced stage, suggesting that clinical complexity may impede timely investigation of respiratory symptoms, reinforcing concerns that medically complex patients may face diagnostic delays despite frequent health system contact [16].

One of the most striking findings of this study was the association between primary care attachment and stage at diagnosis. Patients who were not rostered to a family physician were substantially more likely to present with stage IV disease compared with those formally rostered. Even patients who were “virtually rostered” experienced worse stage distribution than those with traditional enrollment. These findings align with previous research [17–19] demonstrating that continuity of primary care facilitates earlier cancer detection through symptom recognition, referral coordination, and diagnostic follow-up. In the context of lung cancer, where symptoms are often nonspecific and may overlap with benign respiratory disease, the absence of a consistent primary care provider may lead to fragmented care and delayed escalation of investigations. Strengthening access to comprehensive primary care may represent an opportunity to expedite lung cancer diagnosis and therefore an earlier stage.

We observed clear socioeconomic gradients in stage at diagnosis across both household- and neighbourhood-level income measures, although the magnitude of effects was subtle. Patients in the lowest income quintiles were less likely to be diagnosed with stage I disease and more likely to present with advanced-stage cancer. These findings are consistent with previous literature [5,20–23] linking socioeconomic disadvantage to later-stage lung cancer diagnosis, even in countries with universal health coverage. Several mechanisms may explain these findings, including higher prevalence of smoking and occupational exposures, competing life priorities, reduced health literacy, and barriers to accessing diagnostic imaging and specialist care [8,24]. More research in this area would be a valuable addition to identify potentially modifiable factors.

Interestingly, we found that immigrant status was a protective factor against a stage IV diagnosis. This finding is consistent with the “healthy immigrant effect” observed in Canada, whereby immigrants often arrive with better baseline health and lower smoking prevalence compared with the Canadian-born population [25,26]. However, this advantage may attenuate over time, and subgroup-specific analyses by country of origin, or duration of residence, or refugee status may reveal more nuanced patterns. Nevertheless, immigrants were more likely to receive surgery after diagnosis than non-immigrants. Language barriers, cultural differences in treatment preferences, and systemic biases may influence treatment decision-making and warrant further investigation [9,27].

Geographic distance to care was modestly but consistently associated with more advanced stage at diagnosis. Patients residing more than 100 km from cancer centres had less stage I diagnoses, more stage III disease, but fewer stage IV compared with those living within 50 km. This finding aligns with prior studies demonstrating rural–urban disparities in lung cancer outcomes, driven by reduced access to diagnostic imaging, specialist services, and multidisciplinary cancer care [28–30]. Our finding of regional variation across Ontario further supports the anticipated benefit of future health system organization and service availability on patient outcomes. Patients in the Central region of Ontario had higher proportions of advanced-stage disease compared with others, whereas the Southwest region had the lowest incidence of stage I diagnoses, reflecting longstanding disparities in cancer outcomes in specific communities [6,31]. These results highlight a gap in access that may be filled by initiatives such as mobile diagnostic services and targeted screening in underserved regions, that could potentially complement existing patient transportation initiatives [32,33].

Despite accounting for stage, disparities in surgical treatment were evident across age, sex, SES, immigration status, and primary care attachment. Older adults, men, lower neighbourhood income patients, non-immigrants, and those without a rostered family physician were less likely to undergo surgery. These findings echo prior evidence of inequities in lung cancer treatment in Canada and elsewhere [11,34,35]. Whilst some differences may reflect appropriate clinical decision-making related to frailty or comorbidity, the magnitude and consistency of disparities suggest potential under-treatment of certain groups [11]. Structural factors, including referral patterns, patient–provider communication, and implicit bias, may contribute to differential access to surgical care [8,27,36].

Our findings highlight that universal healthcare alone is insufficient to eliminate inequities in lung cancer diagnosis and treatment. Interventions to improve early detection to address upstream social and structural determinants, beyond screening eligibility, are vital to address the imbalance. Expanding organised lung cancer screening programs with proactive outreach to socially disadvantaged populations may help reduce stage disparities, particularly if coupled with primary care integration and patient navigation supports. Strengthening access to longitudinal primary care may yield benefits across the cancer care continuum, from earlier stage at diagnosis to receipt of appropriate treatment.

To our knowledge, this is the first Canadian population-level analysis to examine the relationship between SDOH and lung cancer stage at diagnosis. Key strengths of this study include the use of a large, population-based cohort spanning an extended time frame and encompassing patients treated across multiple institutions and diverse geographic regions within Ontario. However, limitations include lack of individual-level smoking data and aspects of social circumstance such as transportation access and cohabitation status, which may have influenced observed outcomes. Additionally, measures of income and distance were area-based proxies and may not fully capture individual circumstances. Furthermore, we were unable to determine whether lung cancer diagnoses among immigrants occurred before or after arrival in Canada, which may have influenced patterns of health system engagement. The available data also did not permit exploration of heterogeneity within the immigrant population by factors such as immigration class, country of origin, or language proficiency, all of which may shape access to care and treatment decisions.

Conclusions

Despite universal healthcare coverage and the initiation of lung cancer screening, there remains significant social disparity in stage of lung cancer at diagnosis. Efforts should be aimed at a more targeted approach to vulnerable populations and widening access to primary care.

Acknowledgments

This document used data adapted from the Statistics Canada Postal Code Conversion File, which is based on data licenced from Canada Post Corporation, and/or data adapted from the Ontario Ministry of Health Postal Code Conversion File, which contains data copied under licence from ©Canada Post Corporation and Statistics Canada. Parts of this material are based on data and/or information compiled and provided by MOH, CIHI, Ontario Health, and Immigration, Refugees and Citizenship Canada (IRCC). The analyses, conclusions, opinions and statements expressed herein are solely those of the authors and do not reflect those of the funding or data sources; no endorsement is intended or should be inferred. We thank the Toronto Community Health Profiles Partnership for providing access to the Ontario Marginalization Index.