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J Oncol Pract. 2016 June; 12(6): e613–e625.
Published online 2016 May 10. doi:  10.1200/JOP.2015.008508
PMCID: PMC4957257

Association of Breast Cancer Knowledge With Receipt of Guideline-Recommended Breast Cancer Treatment

Rachel A. Freedman, MD, MPH,corresponding author Elena M. Kouri, PhD, Dee W. West, PhD, Joyce Lii, MA, MS, and Nancy L. Keating, MD, MPH

Abstract

Purpose:

Knowledge about one’s breast cancer characteristics is poor, but whether this knowledge affects treatment is uncertain. Among women with breast cancer, we examined whether tumor knowledge was associated with adjuvant treatment receipt.

Methods:

We surveyed a population-based sample of women in Northern California with stage 0 to III breast cancer diagnosed during 2010 to 2011 (participation rate, 68.5%). Interviews were conducted between 4 months and 3 years after diagnosis. Among 414 respondents with stage I to III disease, we examined receipt of guideline-recommended chemotherapy, radiation, and hormonal therapy by reporting correct information about one’s tumor, including stage, estrogen receptor, human epidermal growth factor receptor 2 (HER2), and grade (using registry data for confirmation). We performed multivariate logistic regression to assess the probability of receiving each treatment in relevant patient groups, adjusting for patient and tumor characteristics, and examined the impact of reporting correct tumor information on treatment receipt.

Results:

Among relevant treatment-eligible groups, 81% received chemotherapy, 91% received radiation, and 83% received hormonal therapy. In adjusted analyses, having correct (v incorrect) information for stage and HER2 were associated with chemotherapy receipt (odds ratio [OR], 4.45; 95% CI, 1.50 to 12.50 for stage; OR, 2.70; 95% CI, 1.02 to 7.18 for HER2). Correctly reporting estrogen receptor status was associated with hormonal therapy receipt (OR, 3.91; 95% CI, 1.73 to 8.86), and correctly reporting stage was associated with radiation receipt (OR, 2.76; 95% CI, 1.03 to 7.40).

Conclusion:

Knowledge about one’s tumor characteristics was strongly associated with receipt of recommended therapies. Interventions to improve patients’ knowledge and understanding of their cancers should be tested as a strategy for improving receipt of care.

INTRODUCTION

Knowledge about one’s health condition or the risk of developing a condition has been shown to affect screening rates, satisfaction with care, and possibly outcomes.1-5 Studies have shown that knowledge about cancer overall is poor across populations,5-8 although most prior work on cancer knowledge for patients with breast cancer has focused on understanding treatment options, general treatment rationales, and overall treatment benefits or how strategies in communicating recurrence information may affect treatment choices.5-13 One study suggested that women who were under-treated for breast cancer were less likely than treated women to know that breast cancer treatments (ie, hormonal therapy and chemotherapy) improved survival.8 However, past studies examining cancer knowledge have not focused on how knowing one’s own cancer characteristics may affect treatment receipt.

We previously demonstrated that knowledge about one’s own cancer, including stage and receptor status, is poor for many women with breast cancer, and that black and Hispanic women are less likely than white women to correctly report tumor characteristics.14 Given these findings and the results demonstrating under-treatment of women with suboptimal understanding of general treatment principles,8 we hypothesized that better tumor-specific knowledge may also lead to higher rates of guideline-recommended treatment initiation and adherence. For example, if a woman knows how important hormonal therapy is because it specifically targets the estrogen receptor (ER)–positive tumor she has, perhaps she will be more willing to receive and adhere to therapy. Furthermore, given that racial/ethnic differences in knowledge about one’s breast cancer characteristics14 and benefits of treatments10 exist, understanding whether knowledge differences contribute to disparities in treatment is important.

We surveyed a diverse, population-based sample of women with breast cancer in northern California to assess the association of knowledge about individual tumor characteristics and receipt of recommended adjuvant therapies. We also examined whether racial disparities in treatment receipt, if present, were mediated by breast cancer knowledge.

METHODS

Study Population

We identified 1,118 white, black, and Hispanic women with stage 0 to III breast cancer diagnosed during 2010 to 2011 in Regions 1/8 (San Francisco/Santa Clara Area [nine counties]) and Region 3 (Sacramento Area [13 counties]) of the California Cancer Registry (CCR).15 The registries (both part of the SEER program) uniformly collect information on patient demographics, tumor characteristics, primary treatments, and mortality for all incident cancers in these regions. We obtained study approvals from the CCR, the California Health and Human Services Agency Committee for the Protection of Human Subjects, and the Harvard Medical School Committee on Human Studies.

Survey Administration and Patient Enrollment

As previously described,14 we mailed introductory letters to eligible patients in English and Spanish inviting them to participate in a one-time survey about their breast cancer care. The mailing included a postage-paid opt-out card and a toll-free number to call to participate or opt out. Patients who did not opt out but whom we did not reach by phone received a second mailing. We attempted at least six telephone calls to women at different times and days. Participants provided verbal consent at the start of the survey and received $20 on interview completion. Interviews were conducted between January 17, 2012 and December 3, 2013 over the telephone by a trained interviewer who used computer-assisted telephone interview software. Women were surveyed between 2 to 3 years (87.2%), 1 to 2 years (11.8%), and 6 to 12 months (0.7%) and at 4 months (0.24% [one patient]) after diagnosis.

Survey

Participants were asked about details surrounding their breast cancer diagnosis and treatment and their breast cancer knowledge.14 Questions about knowledge included the following: “What was the stage of your cancer? Was it 0, 1, 2, 3, 4?”; “What was the grade of your cancer? Was it...low grade/well differentiated, or grade 1; intermediate grade, moderately differentiated, or grade 2; or high grade, poorly differentiated, or grade 3?”; “Was your cancer subtype HER2-positive, also called human epidermal growth factor receptor 2–positive?”; and “Was your breast cancer estrogen receptor (ER)-positive?” Patients could answer “I don’t know” for any of these questions. We also asked about treatments received16 and collected information on self-reported race/ethnicity, educational attainment,17 household income,17 insurance at diagnosis,17 health literacy,18 and comorbidity.17

Response Rates

Details about the response rates have been previously published.14 In summary, among 1,118 identified patients, 231 refused participation (20.6%), 317 could not be reached, 68 were deceased/too ill, and 502 women were surveyed. The American Association for Public Opinion Research response rate19 was 47.8% (502/[1,118−68]) and the participation rate among those for whom we had contact information was 68.5% (502/([1,118−68−317]). Two women self-identifying as Asian were excluded because our study focused on white/black/Hispanic patients. Seventy of 136 (52%) Hispanic women were interviewed in Spanish. Respondents and nonrespondents had similar demographic and tumor characteristics (including tumor stage and receptors), except respondents were younger (mean age, 58 v 64 years; P < .001). There were no significant differences in adjuvant treatment receipt according to the CCR for nonrespondents and respondents (data not shown). In a final exclusion step, we removed patients with stage 0 disease (n = 86), because treatment recommendations for preinvasive disease can be variable. The final analytic cohort included 414 patients.

Variables of Interest

We examined receipt of National Comprehensive Cancer Network guideline–recommended20 adjuvant chemotherapy, radiation, and hormonal therapy among relevant groups of women (Appendix Table A1, online only). It is of note that the guidelines for standard treatments did not change during the period when women were diagnosed or interviewed. When assigning treatment-eligible cohorts of patients, we only included patients with more definite indications for each treatment (eg, patients with low-risk tumors were not included in the chemotherapy cohort because they may appropriately not receive chemotherapy). Because past reports have questioned the completeness of registry data21,22 and because of some inconsistencies in report of treatments by patients and the CCR in our cohort (ie, 25% reported taking hormonal therapy when the registry reported no treatment, 24% reported receiving radiation when the registry reported no radiation, and 6% reported receiving chemotherapy when the registry reported no chemotherapy), we defined treatment receipt as having either CCR report of receipt or self-report of treatment receipt: “Did you receive radiation treatment?”; “Did you receive chemotherapy?”; “Did you receive hormonal treatment or anti-estrogen treatments, often given as pills for 5 years?” Because self-reported treatment receipt from diverse patients has been shown to be accurate,23-25 we believed this information would enhance CCR treatment data.

Independent Variables

Our primary independent variable of interest was knowledge of breast cancer characteristics (stage/ER/human epidermal growth factor receptor 2 [HER2]/grade).14 Answers were considered correct if a participant’s answer matched the tumor characteristic according to the CCR or if the CCR result was unknown, not performed, or missing (because of the inability to confirm correctness). Women who reported having stage IV disease (n = 12) were considered to correctly report stage because their cancer (originally diagnosed as stage 0 to III) may have recurred.

Additional variables of interest included self-reported race/ethnicity (non-Hispanic white/non-Hispanic black/Hispanic). Control variables were selected a priori on the basis of clinical relevance or because of previously described associations with treatment (Table 1) and included age, marital status, insurance status at diagnosis, number of comorbidities (past diagnosis of another cancer, diabetes/chronic lung disease/kidney problem/heart disease or stroke), history of depression/psychiatric illness, cancer stage, household income over the last year, educational attainment, and health literacy.18 Health literacy has been associated with adherence, treatment, outcomes,26 and the degree of effective communication27 for various chronic conditions and was included in models examining treatment receipt for this reason.

Table 1.
Participant Characteristics by Receipt of Each Adjuvant Therapy Within Each Treatment Group (N = 414)

Statistical Analysis

We used the χ2, Fisher’s exact, and Kruskal-Wallis tests to assess differences in baseline characteristics by receipt of each adjuvant therapy within each relevant treatment group. We also examined differences in adjuvant treatment receipt by correctly answering questions. We used logistic regression to examine the probability of receipt of each adjuvant therapy separately, first performing a model including race/ethnicity, stage, age, marital status, insurance, comorbidity, depression/psychiatric problem, income, educational attainment, and health literacy (ie, base model). Models examining chemotherapy did not include a variable for insurance because almost all women in this treatment group were insured, and models including this variable were not stable. We then repeated models after sequential inclusion of each correct variable for stage, ER, HER2, and grade in addition to an ordinal variable for having more answers correct (range, 0 to 4). Additional models to test for possible mediation of racial/ethnic differences in therapy by knowledge were not performed because adjuvant therapy receipt did not differ significantly by race/ethnicity.

We performed a series of sensitivity analyses. First, we repeated analyses for chemotherapy receipt after excluding women older than 70 years (n = 30) and radiation receipt after excluding women older than 70 years with stage I ER-positive or progesterone receptor (PR)–positive cancers (n = 32) because of variable (yet often appropriate) practice for these subgroups. In addition, because HER2 status strongly influences recommendations for chemotherapy, we repeated the chemotherapy model after excluding those with unknown HER2 status according to the registry (n = 95, 23% of cases) to more accurately ascertain HER2 correctness (given that those reporting “I don’t know” but who had unknown HER2 status by the CCR were categorized as having correct HER2 in primary models). Last, we repeated all treatment models after excluding those with unknown ER status (3%), HER2 status (23%), or grade (5%) according to the CCR. All patients had stage recorded in the CCR.

RESULTS

The overall characteristics for each treatment-eligible cohort are shown in Table 1, and the characteristics of treatment-eligible patients by receipt of each adjuvant therapy are shown in Table 2. Approximately 44% of the overall sample was white, 31% were black, and 25% were Hispanic. Most (88%) patients had stage I or II disease, and more than half of the patients were younger than 60 years (Table 1). Among 183 chemotherapy-eligible patients, 81% (n = 149) received chemotherapy. Among 255 radiation-eligible patients and 318 hormonal therapy–eligible patients, 91% (n = 233) and 83% (n = 263) received treatment, respectively. In general, higher stage and younger age were significantly associated with hormonal therapy and chemotherapy receipt. Although we observed some numerical differences for treatment receipt by race/ethnicity, these were not statistically significant.

Table 2.
Unadjusted Percentage and Adjusted OR for Receipt of Each Treatment Within Each Treatment-Eligible Group

Table 1 displays the proportion of patients answering each characteristic correctly within each cohort. Overall, the characteristic most frequently reported as correct was ER (58%). Less than 10% of patients answered all tumor questions correctly.

Knowledge and Receipt of Treatment

Unadjusted results for answering questions correctly by receipt of each adjuvant treatment within each group are shown in Figure 1. Correct stage was associated with chemotherapy, correct ER status was associated with hormonal therapy, and correct HER2 status was associated with chemotherapy and hormonal therapy (all P < .05). Correct grade was not associated with treatment receipt.

FIG 1.
Unadjusted proportion (y-axis) receiving each adjuvant treatment within each group by correctly reporting each tumor characteristic. P values by χ2 testing. Blue bars represent receipt of each treatment by women who answered correctly for each ...

Adjusted Results for Receipt of Adjuvant Treatment

In the base models (not including correctly reporting variables; Table 2), adjusted results revealed no significant racial/ethnic differences in adjuvant treatment receipt. The odds for receipt of chemotherapy differed by age and stage, with older (v younger) women having lower odds and those with higher-stage disease having higher odds of chemotherapy. Those with stage II (v I) disease had higher odds for hormonal therapy. In addition, having one comorbid condition (v 0) and reporting a history of depression/emotional/psychiatric problem were associated with higher odds of chemotherapy.

In analyses where correctly reporting treatment variables were added (separately) to base models (Table 2), correctly reporting stage was associated with higher odds of chemotherapy and radiation. Correctly reporting HER2 status was associated with chemotherapy, and correctly reporting ER was associated with higher odds of hormonal therapy. In models assessing the total number of characteristics correctly reported, having more characteristics correct was associated with higher odds of chemotherapy and hormonal therapy. Overall, including knowledge variables did not significantly affect results for other variables in the base model.

In sensitivity analyses, results for chemotherapy receipt after excluding patients older than 70 years were similar, although having more answers correct was no longer significant. Results for the models examining radiation receipt after excluding patients older than 70 years with stage I, hormone receptor–positive tumors were similar. Last, results were also similar after excluding patients whose HER2 status was unknown according to the CCR or whose results for ER, HER2, or grade were unknown in the CCR (data not shown).

DISCUSSION

In this population-based sample of patients with breast cancer with relatively poor knowledge about their own breast cancers, we observed strong associations for correctly reporting breast cancer subtype (ER, HER2) with receipt of guideline-recommended hormonal therapy and chemotherapy, and reporting correct stage was associated with receipt of recommended radiation. Correctly reporting tumor grade was not significantly associated with treatment.

These findings provide initial support for our hypothesis that knowledge of one’s tumor characteristics may help assure that patients initiate and continue adjuvant therapies, although further work will be required to fully understand the direction of these associations. However, it is plausible that patients who understand the mechanism of treatments that target HER2 and ER may be more likely to understand the importance of long courses of trastuzumab or endocrine therapy. In addition, the association of knowledge about one’s stage but not other tumor characteristics with radiation was not unexpected, because most recommendations for radiation are still made on the basis of anatomic stage rather than tumor subtype.20 The lack of association for grade and treatment was also not surprising; providers may not emphasize grade during treatment discussions as much as they may highlight subtype and stage.

Although our observations are provocative and consistent with other work describing associations for understanding general treatment rationales and benefits of therapy with receipt of care,5,6,8,28,29 broader interpretation of our results is limited by a lack of detailed information on treatment discussions, information on trastuzumab, patient preferences, and if/how information was conveyed to patients. In addition to the potential importance of individualized tumor information, others have suggested that the ways recurrence and survival risks are presented may also impact receipt of chemotherapy.11-13 Our findings support the need for further study of how knowledge about one’s own disease specifically affects care and outcomes, with inclusion of factors such as information/learning preferences, detailed assessment of health literacy, social supports and whether they were present during discussions, and understanding other potential barriers to care. Certainly, improving knowledge about one’s tumor characteristics is a modifiable factor that could be addressed in intervention studies.

Reassuringly, we did not observe differences in receipt of treatment by race/ethnicity in our study and were thus not able to examine whether knowledge mediated any racial/ethnic disparities in care. This may be because of the relatively small numbers of patients in the treatment-eligible subgroups or because of our focus on a single geographic area. Nevertheless, many other studies have documented persistent disparities in treatment receipt,30-38 and understanding how differences in knowledge may affect disparities among larger and broader cohorts is essential. We did observe differences in treatment by stage and age, consistent with other studies.34,37,39-42 Our findings of higher odds of chemotherapy for those with one comorbid condition or psychiatric disorders are contrary to other reports37,41-44 but may have been observed because our comorbidity and depression measures did not fully capture treatment-limiting conditions or because one comorbid condition and/or mild emotional disorders were unlikely to limit treatment receipt.

To our knowledge, this is the first study to examine women’s knowledge about their own disease characteristics and receipt of treatments. We surveyed a large number of women in their primary language and collected individualized information on several sociodemographic factors. However, we acknowledge several limitations. First, our definitions of correctly reporting tumor characteristics relied on the accuracy of registry data. Nevertheless, prior studies have shown relatively accurate tumor stage reporting in registries compared with medical records.21,45 To avoid misclassification of women who reported information about their tumors when CCR data were not available, we considered answers correct whenever registry data were missing/unknown for that characteristic. Furthermore, we categorized women as having received treatment if the registry or patient reported receiving it, in the attempt to capture all possible treatment received. We also repeated analyses after excluding those with unknown HER2 status (and other unknown variables) in the CCR data given the relatively high proportion of these cases and observed even stronger associations of HER2 knowledge and receipt of systemic therapy. Of note, we focused on ER-positive (rather than PR) disease as the primary subtype indicated for hormonal therapy because only one of 414 patients had ER-negative and PR-positive disease. Second, although population based, the numbers of women in certain subgroups were small and almost all women were insured, limiting examination of certain variables. Third, we cannot rule out nonresponse bias, although responders were similar to nonresponders by race/ethnicity and tumor characteristics.14 Fourth, because we surveyed women up to 3 years after their breast cancer diagnosis, recall bias may have contributed to the lack of knowledge for some women. However, year of diagnosis was not significantly associated with responses for knowledge questions (data not shown). Fifth, we did not have detailed information about short- or long-term adherence to treatment or the presence of treatment delays. Also, we lacked information about some patient characteristics (eg, numeracy) and beliefs (eg, fear of treatment), although our study nevertheless included rich patient information. Finally, although our results demonstrate a link between knowledge about one’s tumor and receipt of therapy, whether a woman knew her tumor characteristics because she received treatment or whether she received treatment as a result of that knowledge is uncertain. Further study will be required to better understand the direction of these associations. In addition, the relationship between knowledge and treatment may be mediated by multiple factors, such as patient-provider communication, educational support, a patient’s social network, information-seeking behaviors, coping skills, and health literacy needs. We did not have information about these important factors in our survey.

In summary, our findings underscore the major knowledge deficits women had with regard to their own cancers and suggest that this knowledge may be important in receipt of guideline-recommended treatments. Our observations highlight the need for further study of the clinical, emotional, and social consequences of poor knowledge and how we can improve information delivery to patients. Interventions to improve patients’ knowledge and understanding of their cancers should be tested as a strategy for improving cancer care.

Acknowledgment

Supported by Susan G. Komen (N.L.K., R.A.F.), an American Cancer Society Mentored Research Scholar Grant (R.A.F.), and National Cancer Institute Grant No. K24CA181510 (N.L.K.). We thank the study participants and the California Cancer Registry and thank Ana Guerrero for assistance with interviews. The collection of cancer incidence data used in this study was supported by the California Department of Public Health as part of the statewide cancer reporting program mandated by California Health and Safety Code Section 103885; the National Cancer Institute’s SEER Program under contract HHSN261201000140C awarded to the Cancer Prevention Institute of California, contract HHSN261201000035C awarded to the University of Southern California, and contract HHSN261201000034C awarded to the Public Health Institute; and the Centers for Disease Control and Prevention’s National Program of Cancer Registries, under agreement U58DP003862-01 awarded to the California Department of Public Health. The ideas and opinions expressed herein are those of the author(s) and endorsement by the State of California, Department of Public Health, the National Cancer Institute, and the Centers for Disease Control and Prevention or their Contractors and Subcontractors is not intended nor should be inferred.

Appendix

Table A1.

TreatmentEligibility for Treatment Group
(deemed eligible if any of the following present)
Subcohort Sample Size
Adjuvant chemotherapyStage IIB, any subtypen = 183
Stage III, any subtype
Tumor > 1 cm if ER- and PR-negative
Tumor > 1 cm if HER2-positive
Adjuvant radiation therapyBCS-treated (stage I-III)n = 255
Unilateral or bilateral mastectomy and stage III disease (postmastectomy radiation)
Adjuvant hormonal therapyAny ER- or PR-positive cancer that is stage I (tumor ≥ 1 cm), stage II, or stage IIIn = 318

Eligible Patient Groups for Examining Receipt of Guideline-Recommended Therapies20

NOTE. Patients could be included in more than one treatment group, depending on disease characteristics.

Abbreviations: BCS, breast-conserving surgery; ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; PR, progesterone receptor.

AUTHOR CONTRIBUTIONS

Conception and design: Rachel A. Freedman, Elena M. Kouri, Dee W. West, Nancy L. Keating

Financial support: Rachel A. Freedman, Nancy L. Keating

Administrative support: All authors

Provision of study materials or patients: Dee W. West

Collection and assembly of data: All authors

Data analysis and interpretation: All authors

Manuscript writing: All authors

Final approval of manuscript: All authors

AUTHORS’ DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

Association of Breast Cancer Knowledge With Receipt of Guideline-Recommended Breast Cancer Treatment

The following represents disclosure information provided by authors of this manuscript. All relationships are considered compensated. Relationships are self-held unless noted. I = Immediate Family Member, Inst = My Institution. Relationships may not relate to the subject matter of this manuscript. For more information about ASCO's conflict of interest policy, please refer to www.asco.org/rwc or jop.ascopubs.org/site/misc/ifc.xhtml.

Rachel A. Freedman

Research Funding: Puma Biotechnology (Inst), Genentech (Inst), Eisai (Inst)

Elena M. Kouri

No relationship to disclose

Dee W. West

No relationship to disclose

Joyce Lii

No relationship to disclose

Nancy L. Keating

No relationship to disclose

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