Chapter 4: RESULTS 69
4.6 MULTILEVEL MULTINOMIAL LOGIT REGRESSION MODEL WITH
4.6.9 Discussion and partial conclusion
In this section we present the results obtained from the analysis of multilevel multi- nomial model where we fitted three different models in classical approach and the best model was selected for further analysis in Bayesian approach using WinBUGS software. The essence is to be able to compare the result of the classical approach
with that of Bayesian approach. In Bayesian paradigm, we set up two different models, namely model with blocking and over-relaxation and model (M1) without blocking and over-relaxation (denoted M2). It was mentioned in the literature that model with blocking sometimes aids convergence (Lesaffre & Lawson, 2012), in this thesis we incorporated blocking with over-relaxation in order to see it’s effect on blocking. For each model we obtained deviance information criteria (DIC), so as to select the best model, the model without blocking (M2) appears to be the best model as it has the lower DIC. This findings are in line with those contained in the literature.
In this study two types of the multilevel models were implemented, namely the fre- quentist and the Bayesian multilevel models and their results were compared. The results obtained from both approaches are identical. At the end of this study, the results showed no significant difference between Bayesian multilevel and classical multilevel approach. One thing that is unique is that it is difficult to compare the result from Bayesian and classical because the former make use of credible interval while the latter uses confidence interval. The non-informative prior models utilized inn the Bayesian approach could have accounted for the similarities between the two approaches. The central aim of the current study is to investigate the associa- tion of SES and biological characteristics for histological type of breast tumor among patients diagnosed of breast cancer in western Nigeria using multilevel multino- mial regression analysis. The most significant observation we found in this study was that age of occurrence of breast cancer in this environment, the mean age of the patients was 42.2 years, this is similar to those of several Nigerian institutions which have been studies in the literature. Among these studies, Adebamowo re- ported 43 years (Adebamowo & Adekunle, 1999), Ikpatt et.al 42.7 years (Ikpat et al., 2002) and 44.9 years by Ebughe.et al (Ebughe et al., 2013a). But the situation is differ- ent in countries with substantially mixed blacks and Caucasians like United States and South Africa, variation is noticed in both incidence and mean age of breast can- cer occurrence (Fregene & Newman, 2005; Anderson et al., 2006). Previous studies have mentioned the peculiarities of breast cancer patients among women of African such as genetic factors and reproductive factors. In our study, there is a correla- tion between the histological type and histologic grade, breast cancer type as well as educational status. This simply means that reproductive and biological factors may determine histologic type of tumors. Other studies have also shown similar result (Ursin et al., 2005; Okobia et al., 2005; Kotsopoulos et al., 2010). But our re- sult is contrary to what is obtainable in other part of Nigeria as reported by (Ebughe et al., 2013b) that reproductive factors may not determine histologic types and bio- logical behavior. Hence, we can attribute this fact that environmental factors may have brought about this changes in the context of breast cancer in Nigeria. The pro-
portions of patients with grade II disease decreased with age, and younger patients were more likely to be diagnosed with a higher grade in this environment. This may be attributed to poor breast cancer screening in young women, as the incidence is high in this age group. In addition, younger patients were more likely to be prone to infiltrating duct carcinoma than the elderly patients, an observations that is sup- ported and consistent with other studies (Chen et al., 2016). It was also found that malignant breast tumor was significant and it happen to be the most prominent type of breast cancer in this environment. This explain why majority of breast cancer pa- tients in this environment are subjected to surgery treatment since the cancer has gotten to a higher level which can only be managed by surgical operation.
The result of Bayesian analysis showed that age group 35-49 years and education were significantly associated with histologic types. We found that patients with at least high school are 9.4 times more likely to have one histologic type of tumor dis- ease than their counterpart. Histologic type of tumor might have resulted from their exposure in advancement in life without observing caution to health management.
Although, our study did not investigate the influence of education on breast can- cer, a study conducted by (Hussain et al., 2008) evaluated the effect of education on in situ and invasive breast cancer risk using Sweden Family-Cancer Database.
Their findings revealed that significant increased risk for in-situ and invasive breast cancer associated with high educational levels. Additionally, previous studies have provided possible explanation for these findings, that highly educated women or women with high socio economic status (SES) are likely to obtain routine breast can- cer screening as a result of having access to preventive healthcare (Akinyemiju et al., 2015).
In addition, previous studies also found that a high level of education was signifi- cantly associated with decreased incidence of high risk ductal breast cancer among postmenopausal women only. Combining this with our study, these finding indi- cates heterogeneity in the association between education and breast cancer risk fac- tors exists not only by histologic type and age at diagnosis, but also tumor charac- teristics (Dalton et al., 2006).
The current study was not without limitations. A few limitations should be consid- ered while interpreting the results from this study, as data collected does not con- tain information regarding regarding adjuvant chemotherapy or endocrine therapy.
Hence, this may have affected our results. In summary, we found that age, his- tologic grade, breast cancer type were associated with histological type of tumor.
Also, consistent with previous findings, our results indicate that the associations be- tween biological factors and the risk of breast cancer differ by histological types of
the tumor. Certain histological types occurred with a significantly higher proportion shortly after women of this geopolitical zone have given birth, which may be as a result of exposure to hazard like chemical and radiation. More interesting was that women with at least high school were more likely to be diagnosed with histologic type, which is a new and unexpected findings in this part of Nigeria. One explana- tion for these result may be that women with at least high school education present their breast cancer cases to medical practitioners than the less educated women hav- ing it in mind that this study uses hospital data. In addition, Bayesian multilevel multinomial regression model helps in selecting the most significant factors between histological type and socio economic status (SES) and biological characteristics of breast cancer tumors as compared to classical multilevel multinomial.