Utilization of Lymph Node Dissection, Race/Ethnicity, and Breast Cancer Outcomes | Page 2
Published Online: October 23, 2013
Zhannat Z. Nurgalieva, MD, PhD; Luisa Franzini, PhD; Robert O. Morgan, PhD; Sally W. Vernon, PhD; and Xianglin L. Du, MD, PhD
We used χ2 testing to compare the differences in categorical variables and proportions between patients who underwent SLNB alone and patients who underwent SLNB with complete ALND. In preliminary analyses, we compared the outcomes of patients undergoing SLNB alone with those of patients undergoing SLNB with complete ALND. We also performed univariate analyses to determine the influence of patient, tumor, and treatment factors with known or potential prognostic value on OS and DSS as determined by the Kaplan-Meier method. Variables subjected to univariate analysis included age (continuous); socioeconomic status; comorbidity index17-21; tumor grade (low/intermediate vs high); tumor size (T1-T3); estrogen receptor and progesterone receptor status (positive, negative, unknown); use of chemotherapy; use of radiotherapy after surgery (yes vs no); year of diagnosis(split, before 2000 and after 2000); and use of ALND. Significant factors from the univariate analysis were included in a multivariate Cox proportional hazard model to identify significant predictors of OS and DSS. In the unadjusted model (model 1) race is the only predictor.The covariates age and tumor size were analyzed as continuous variables in the multivariate models. Covariates added in our regression models included patient and tumor characteristics (age, year of diagnosis, treatment [chemotherapy, surgery, radiation], tumor stage, tumor size, tumor grade and number of positive lymph nodes, diameter of positive lymph nodes, comorbidities, socioeconomic status) (model 2); and receipt of nodal surgery (model 3). Hazard ratios (HRs) and 95% confidence intervals (CIs) were obtained for all regressions. Analyses were performed using SAS release 9.2 (SAS Institute Inc, Cary, North Carolina). All tests were 2-tailed with statistical significance set at P <.05.
Of the 24,961 women in the SEER database who underwent SLNB as part of their surgical treatment for BC from 1998 to 2005, 5364 (21%) had nodal metastases and comprised the cohort we analyzed. Of the patients in the cohort, 1028 (19%) underwent SLNB alone and 4336 (81%) underwent SLNB with a complete ALND. Most patients (n = 4098) had macrometastasis, and 1831 patients had micrometastasis.
Proportions of patients receiving SLNB alone or receiving SLNB with a complete ALND were not statistically different among women of different racial/ethnic backgrounds (P = .8) in a cohort of BC patients restricted to those with nodal metastases. A higher proportion of patients underwent SLNB alone if they were diagnosed after 2000 (81.7% vs 18.3%). Patients who underwent SLNB alone rather than SLNB with complete ALND were more likely to have smaller (median tumor size, 15 mm vs 20 mm) or low-grade tumors (69.2% low/intermediate vs 23.6% high grade) (Table 1). Most patients (84.2%) who underwent SLNB alone had breast-conservation surgery. The median number of lymph nodes removed during surgery was 2 in the patients who underwent SLNB alone and 12 in those who underwent SLNB with complete ALND (P <.0001). The mean number of lymph nodes removed was 3.9 (range, 1-32 nodes) in the SLNB-alone group and 13 (range, 1-52 nodes) in the SLNB plus ALND group.
Of the patients undergoing SLNB alone, 52.4% had micrometastases, compared with only 22.1% of the patients undergoing SLNB with complete ALND. Table 2 shows a multivariate analysis for factors associated with undergoing SLNB alone. Patients were more likely to undergo SLNB alone compared with SLNB with complete ALND if they had smaller or low-grade tumors, had micrometastases, had positive estrogen receptor status, and were undergoing segmental mastectomy. Of the study population, 551 patients (10.5%) had died of any cause, and 297 patients (5.5%) had died of BC. Overall survival was not greatly different for patients undergoing SLNB alone compared with those undergoing SLNB with complete ALND in the entire cohort and in patients with micrometastases or macrometastases. Table 3 shows the clinical and pathologic factors affecting OS and DSS.
Patients of African American descent or of Hispanic origin had reduced OS after adjusting for selected covariates. Older women or those with macrometastases, highgrade tumors, larger tumors, negative estrogen receptor status, or more positive lymph nodes found during surgery had reduced OS. Adjusting for nodal surgery did not reduce racial/ethnic disparities in OS. Patients of Hispanic origin who were older or who had high-grade tumors, larger tumors, or negative estrogen receptor or progesterone receptor status; who underwent complete ALND after SLNB; or who had more positive lymph nodes found during surgery had reduced DSS. Disease-specific survival was decreased in patients with macrometastasis (not statistically significant). Adjusting for nodal surgery did not reduce racial/ethnic disparities in DSS.
Yi and colleagues4 recently examined differences in survival for patients with nodal disease undergoing SLNB alone versus SLNB with complete ALND. Similar to their results, we found no significant differences in utilization of SLNB alone or SLNB with a complete ALND between Caucasian and African American older BC patients in a cohort restricted to those with micrometastasis and macrometastasis in sentinel lymph nodes. In our study, this observation also held true for Hispanics and Asians/Pacific Islanders. Our study is unique in that it is one of the first reports of health outcomes in older BC patients with nodal disease for Hispanics, Asians, and Pacific Islanders. Previously mentioned studies did observe racial/ethnic disparities in utilization or quality of nodal surgery.1,5-8 This difference probably reflects the fact that their purpose was not to address BC survival with receipt of nodal surgery; therefore, they did not restrict their study population to only those with nodal disease. Similar to the findings reported by Bilimoria and colleagues3 and Yi and colleagues,4 our study suggests that patients are more likely to receive SLNB alone if they undergo breast-conservation therapy, are older, and have smaller primary tumors.
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