This study shows that in the Netherlands, a country with assumed equal access to care, breast cancer patients with high SES were less likely to undergo SNB and, in the oldest group, more likely to receive additionally lymph node dissection. Furthermore, in patients aged 50–75 years the use of breast-conserving surgery and chemotherapy was significantly related to SES, although the absolute differences between the SES groups were generally small. In early-stage breast cancer, the use of breast-conserving surgery (+radiotherapy) was the highest in patients with high SES. This could not be fully explained by patient age, year of diagnosis and T-stage. Among the patients with node-positive breast cancer, a higher use of chemotherapy was observed among those with high SES. This difference, however, disappeared after adjustment for stage, age and year of diagnosis.
A prior US study showed higher rates of lymph node biopsy/sampling, that is, either axillary lymph node dissection or SNB, in areas where the education level was higher, although the absolute differences were small (Halpern et al, 2009
). Our data suggest a poorer staging of the axillary lymph nodes and abandoning surgery in the armpit in patients with high SES. We cannot explain this observation as we expected the rates to increase with higher SES owing to — among others — better understanding of the importance of axillary staging. Possibly, patients with high SES are more conscious of the side effects of lymph node dissection, such as lymph oedema, and therefore are more inclined not to undergo this therapy. Previously, older age was associated with reduced likelihood of receiving lymph node biopsy (Halpern et al, 2009
), but the mean age differed by only 3 years in our study, suggesting that age only little affected the staging procedure. Another study stated that among women undergoing breast-conserving surgery, those with comorbid conditions were less likely to receive axillary dissection (Louwman et al, 2005
). As cancer patients with high SES have fewer comorbidities (Louwman et al, 2010
), higher rates of axillary dissection would be expected among high-SES patients. We had no information on comorbidities in this study, but it probably has not contributed to the lower rates of SNB in high-SES patients in our study population. Besides, in the US, patients treated in hospitals with higher patient volumes were more likely to receive lymph node biopsy (Halpern et al, 2009
). Possibly this has affected our results as well. Also, in the Netherlands, staging procedures and type of surgery depended on hospital characteristics, such as volume, with reducing differences over time (van Steenbergen et al, 2010
). It should be noted, however, that absolute differences in our study were small and that statistical significance may have resulted from the large number of patients.
Our results on treatment selection are in line with and the order of magnitude is fairly similar to studies from Denmark and the UK. These studies have shown that women with a lower SES had higher mastectomy rates (Norredam et al, 1998
; Taylor and Cheng, 2003
; Henley et al, 2005
) and lower breast-conserving surgery rates (Taylor and Cheng, 2003
; Downing et al, 2007
; Raine et al, 2010
), although an age-dependent association has been observed as well (Thomson et al, 2001
). Adjustment for stage explained the higher mastectomy rates observed in low SES (Henley et al, 2005
), whereas the association remained significant after stratification by tumour size (Taylor and Cheng, 2003
) and stage (our study, early stage (data not shown)). This implies that type of surgery chosen for the SES groups is not fully explained by stage and age in early-stage disease. Because of higher prevalence of concomitant diseases in patients with low SES (Louwman et al, 2010
), type of surgery is expected to be less invasive owing to the poor general condition in low SES patients. In fact, we observed higher invasive surgery (mastectomy) rates in low SES. Presence of comorbidities might also be indicative of mastectomy to avoid the effects of radiotherapy, but this has not been studied before. A Northern Italian study found that presence of comorbidities reduced the odds of receiving radiotherapy after breast-conserving surgery (Rosato et al, 2009
). Besides, that study also reported no educational differences in treatment of early-stage breast cancer after adjustment for comorbidities and hospital characteristics (Rosato et al, 2009
). As discussed previously, hospital characteristics were affecting treatment selection, including type of surgery and use of radiotherapy, in the Netherlands as well (Vulto et al, 2005
; Siesling et al, 2007
; van Steenbergen et al, 2010
), but we could not take these into account in our analyses. Nor were we able to investigate the contributions of ER status or grade, but previously these factors were reported to be not associated to SES (Henley et al, 2005
). More active involvement of the patient in decision making led to higher mastectomy rates (Katz et al, 2005
), but the effects in the Netherlands remain to be studied.
In our study, in accordance with the Dutch treatment guidelines (Oncoline. www.oncoline.nl
.), nearly all patients undergoing breast-conserving surgery received additional radiotherapy (97%) and no differences were observed between the SES groups. Our results are in line with a study from the UK, in which the odds of receiving adjuvant radiotherapy was not associated with deprivation (Downing et al, 2007
). Compared with the US, our rates of adjuvant radiotherapy are high (97% vs
73%) (Smith et al, 2010
). Furthermore, in the US, large SES differences were observed, with adjuvant radiotherapy rates of 67% in patients with low SES vs
78% in those with high SES in the period 1991–2002, which were not explained by stage, hormone receptor status, grade, chemotherapy, comorbidity and surgeon characteristics (Hershman et al, 2008
). Similar differences were observed in another US study investigating adjuvant radiotherapy rates according to race, which reported 74% in whites vs
65% in blacks (Smith et al, 2010
), which remained also significant after adjustment for demographic, clinical (including comorbidities) and socioeconomic covariates.
Previous studies have reported inconsistent results with respect to the associations between SES and adjuvant radiotherapy, chemotherapy and endocrine treatment (Macleod et al, 2000
; Taylor and Cheng, 2003
; Downing et al, 2007
), with higher rates in high SES in some studies but no association in others (Macleod et al, 2000
; Downing et al, 2007
; Bhargava and Du, 2009
). Low educational level was associated with reduced doses of chemotherapy, whereas presence of comorbidities was not associated (Griggs et al, 2007
). No data were available on chemotherapy doses from the Netherlands Cancer Registry. Besides, we have used the pathological staging supplemented with clinical TNM in case postoperative data were missing. As we were not able to classify chemotherapy as adjuvant or neoadjuvant, the staging may not be completely correct for the patients who received neoadjuvant chemotherapy.
Higher education predicted hormonal therapy use in older US breast cancer survivors (Yen et al, 2011
). For those on hormonal therapy, wealthier women and women with insurance coverage for some or all medication costs were more likely to receive an aromatase inhibitor, which is prescribed by the American Society for Clinical Oncology (ASCO) (Yen et al, 2011
). Owing to the Dutch obligatory health insurance for every inhabitant, insurance status is unlikely to affect treatment selection. This is in line with our finding that hormonal therapy was not related to SES in our study.
Unfortunately, patient preferences in itself could not be taken into account in this study. For example, the choice of mastectomy depends on the interplay between the surgeon's recommendations and patients' preferences for treatment (Hawley, 2010
). The role of patient decision making (Smith et al, 2009
) is likely to be influenced by health literacy, that is, ‘The degree to which individuals have the capacity to obtain, process, and understand basic health information and services needed to make appropriate health decisions' (National Network of Libraries of Medicine, 2010
). Low health literacy may lead to treatment options that are not fully understood, and therefore some patients may not receive the most appropriate treatment for their medical condition (Merriman et al, 2002
). As SES can be linked with education, those with low SES are expected to be more vulnerable to low health literacy. A solution towards solving this might be to focus more on clear and adapted communication by health-care providers. In contrast, some patients do not want to be very involved in decision making (Lantz et al, 2005
; Levinson et al, 2005
Our study findings might be influenced by several limitations. First, we had no information on the presence of comorbidities, which may have affected therapy selection. Second, data on grade, ER status and PR status were not available, which might have affected our results. Third, we had no information on hospital characteristics, which affected therapy selection in Italy and the Netherlands; however, in the latter study, regional and hospital variation reduced over time (Rosato et al, 2009
; van Steenbergen et al, 2010
). Fourth, in this study we have used a measure of SES based on 6-digit postal code of the residential area. Our results may therefore be subject to ecological fallacy. Furthermore, our findings may be explained by some residual confounding. Although this measure of SES is not based on individual data on income, education or occupation, it covers a relatively small geographical area and thus is likely to represent a reliable approximation of individual SES. Previous studies in the Netherlands have proven that socioeconomic differences based on neighbourhood data tend to reflect socioeconomic differences accurately at the individual level (Bos et al, 2000
; Smits et al, 2001
). Furthermore, as the measure of SES used in this study is based on several outcomes, it also applies to older women (born before 1955), although their occupation or education does not always properly reflect their social class (Berkman and Macintyre, 1997
Nevertheless, we have used population-based nationwide data, including all breast cancer patients from the Netherlands. We have thus provided a complete overview of the association between SES and the staging and treatment selection of breast cancer, which has not been done before.