The method by which breast cancer is detected significantly influences clinical outcomes in women aged 40 years and older. Differences in access to screening services across age groups have led to varied patterns of detection, staging at diagnosis, treatment decisions and mortality rates. Retrospective analysis of over 800 cases at a Canadian tertiary referral centre provided insight into the association between method of detection and patient outcomes, taking into account the national screening guidelines that limit routine mammography in certain age groups.
Detection Method and Stage at Diagnosis
The method of detection was categorised as screening, symptomatic or incidental. Screening detection referred to cancers identified through routine mammography in the absence of symptoms, whereas symptomatic detection involved cancers found following clinical signs such as palpable lumps or nipple changes. Incidental detection involved diagnosis during imaging for unrelated issues. Among the 821 patients included, 47.9% had screen-detected cancer, 50.1% had symptom-detected cancer and 2.1% had incidental findings.
Detection method was closely tied to age. Symptom-detected cancers were most frequent in the less-screened age groups of 40–49 years and 75 years or older, accounting for over 70% of diagnoses in each group. In contrast, screen-detected cancers were more common in the routinely screened age groups of 50–59 and 60–74 years. Advanced cancers, defined as stage IIA or greater, were present in 44% of all cases, with 65% of these being symptom-detected compared with only 21.4% of screen-detected cases.
Early-stage cancers (stage 0, IA or IB) were much more frequently diagnosed in screen-detected patients (78.6%) than in those with symptom-detected cancers (34.1%). Among the screen-detected group, the proportion of advanced cancer was significantly lower across all age groups. In the 40–49 age bracket, advanced cancer occurred in 6.1% of screen-detected cases compared to 68% of symptom-detected ones. The proportion of advanced cancers remained consistently higher in symptom-detected patients across all other age brackets.
Treatment and Mortality Outcomes
Differences in cancer stage at diagnosis translated into differences in treatment. Mastectomy was more common among symptom-detected patients, with an adjusted odds ratio of 2.20. Overall, 38.2% of screen-detected patients underwent mastectomy compared with 59.2% of those with symptom-detected cancers. This pattern was particularly pronounced in the older and less-screened age groups. In patients aged 60–74 and those aged 75 or older, symptom-detected cancers had a significantly higher likelihood of being treated with mastectomy than those detected through screening.
Chemotherapy was administered at similar rates regardless of detection method when adjusted for age and stage, although multivariable analysis showed a greater likelihood of chemotherapy among patients with higher-stage cancers and those diagnosed at an older age. Interval cancers, defined as cancers diagnosed within 24 months of a normal screening mammogram, accounted for 8.65% of cases, with many of these patients having had no mammography within the past two years.
Mortality patterns mirrored detection method and stage. Of the 153 deaths recorded over an average follow-up period of 6.7 years, 82 were attributed to breast cancer. The proportion of breast cancer–related deaths was higher among symptom-detected patients. Among women aged 40–49, all deaths occurred in those with symptom-detected cancers. In the total cohort, 14.5% of screen-detected patients died, compared with 21.7% of those whose cancer was detected through symptoms. The hazard ratio for breast cancer–related death was 1.63 for symptom-detected patients, after adjusting for age at diagnosis.
A large proportion of women in the study had either never undergone screening mammography or had not been screened within the previous two years. Only 60% of eligible women participated in regular screening. Among patients with a history of mammography, 86% had not been screened within the recommended interval. These patterns suggest gaps in access and adherence to screening guidelines, particularly for women outside the 50–74-year bracket.
Implications for Screening Policy
The outcomes observed in the less-screened age groups highlight the potential impact of expanding access to screening mammography. Women aged 40–49 and those aged 75 and older were more likely to be diagnosed at later stages, require mastectomy and experience breast cancer–related mortality. Despite comprising a smaller proportion of total cases, these groups accounted for a disproportionately high number of advanced cancers and deaths.
Must Read: Impact of Mammography on Late-Stage Diagnosis
The data support the effectiveness of screening mammography in reducing the burden of advanced disease and associated treatments. Screen-detected cancers were associated with lower odds of advanced stage, less invasive surgery and improved survival. This was consistent even after accounting for variables such as age and tumour stage.
Multivariable analysis confirmed that method of detection was a key factor in clinical outcomes. The odds of a higher-stage diagnosis were 6.40 times greater for symptom-detected cancers. Patients with symptom-detected cancers also had a nearly two-fold increase in the likelihood of receiving chemotherapy. These findings underline the importance of early detection not only in improving survival but also in reducing the intensity and cost of treatment.
Detection method has a profound impact on the clinical outcomes of breast cancer in women aged 40 years and older. Screen-detected cancers are more likely to be identified at an early stage, are less frequently treated with mastectomy and are associated with reduced mortality. Less-screened age groups experience worse outcomes due to later detection and more advanced disease at diagnosis. Enhancing access to routine mammographic screening, especially in underserved age groups, could substantially reduce the burden of breast cancer by enabling earlier intervention and minimising the need for aggressive treatments.
Source: Radiology: Imaging Cancer
Image Credit: iStock
