Pathology Characteristics of Lymphomas in Rwanda: A Retrospective Study

Background: Lymphomas have been a global challenge for many decades and despite measures for prevention and management, the incidence continues to increase. There are two main categories, which are Non-Hodgkin's Lymphomas and Hodgkin's Lymphomas and most common etiologies are environmental, genetic alteration, radiation and some viruses. Objective: To describe pathology characteristics of lymphomas in Rwanda based on Hematoxylin and Eosin stained glass slides and immuno histo chemistry, and classify them according to clinical aggressiveness. Patients and Methods: We conducted a retrospective observational and descriptive study from January 2013 to December 2019. Lymphoma cases were retrieved together with relevant clinical and pathological information, and reviewed by independent pathologists. Histological diagnosis was classified according to the 2008 World Health Organization system in order to assign clinical aggressiveness of the lymphoma. Results: Three hundred and six lymphoma cases were enrolled. Males contributed to 57% of all reviewed case, and slightly over 50% were young aged ≤35 years. Approximately 191 (62%) of cases were nodal lymphomas. Approximately one fifth (18%) of lymphoma cases were HIV positive. Most 213(70%) cases were Non-Hodgkin's Lymphomas of aggressive forms 164(77%). Among 164 cases of aggressive Non-Hodgkin's Lymphomas, diffuse large B cell lymphoma was the leading subtype 91(55.5%), followed by solid lymphoblastic lymphoma 32(19.5%) and Burkitt lymphoma 17(10.4%). Among all Hodgkin lymphoma cases, 90(97%) were classical Hodgkin lymphomaof nodular sclerosis subtype. Hodgkin lymphoma patients were younger compared to Non-Hodgkin's Lymphomas patients (mean age of 24.78±16.3 years versus 38.6±22. 5years, p=.000). Conclusion: Substantial proportion of Lymphomapatients in Rwanda were also HIV positive. Interestingly, Non-Hodgkin's Lymphomas in Rwanda are predominated by the most aggressive forms, and these mostly affect a younger population. Optimal characterisation of such cases, using advanced methods, is recommended.

Thus, available data on the distribution of lymphomas in Rwanda are from 15 years back. Since then, huge changes in the diagnosis, classification and treatment of lymphoma have taken place around the world, thanks to the introduction of immunological and genetic testing among others. More specifically, in Rwanda, immunohistochemistry has recently been introduced for the confirmation and / or sub typing of lymphoma cases.
This study aimed at assessing the current clinical and pathological features of lymphoma in patients diagnosed with lymphoma in Rwanda on the basis of morphology and the newly introduced immunohistochemistry. Trends observed in the data generated will likely inform clinicians, researchers and healthcare administrators of areas to focus on in their interventions.

BACKGROUND
C ancer is a burden worldwide with 17.5 million cases and more than 8.7million deaths in 2015. 1 In Africa, between 2012 and 2030, the number of new cancer cases per year is expected to increase by 70%. 2 In sub-Saharan Africa, more than 456,000 deaths were caused by cancer in 2012 and a double is predicted in 2030. 3 Lymphomas are categorised in two main groups, Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL). In 2015, the global incidence of NHL and HL was 666,000 and 231,000 cases, respectively, while deaths were 78,000 and 24,000 cases, respectively. 1 In Rwanda, a survey done for the period of 1979-1987 showed that NHL represented 83.5% of all lymphomas. 4 The most recent epidemiological study on cancer in Rwanda, covering the period of 2000 to 2004 showed that lymphoma constituted 25.3% of all cancers and was predominated(79.8%)by NHLs. 5 Type and Setting of the Study We conducted a retrospective descriptive study on lymphomas cases diagnosed in Rwanda during the period of 2013-2019. The main stay of this study was Butaro Cancer Centre of Excellence (BCCOE) which receives the vast majority of lymphomas cases in Rwanda for diagnosis and/or immunohistochemistry, as it is the main centre for cancer chemotherapy in the country.

Data Collection
Data were obtained from BCCOE histopathology archives. Permanent hematoxylin and eosin (H&E) and immunoperoxidase-stained slides were re-evaluated for diagnosis confirmation by 2 independent pathologists. In case of divergent conclusions, the two pathologists made a consensus diagnosis. Cases were categorized into HL and NHL. We used the 2008 WHO classification 6 to categorize the cases according to their clinical aggressiveness. The current 2016 WHO classification 7 in which genomic profiling is an important component, couldn't be used in this study because genomic profiling is not yet incorporated in clinical services in Rwanda. Lymphoma staging data was not included as this information was missing from most files consulted.

Data Management and Statistical Analysis
Demographic, clinical, morphology and immunohistochemistry data were entered into data collection sheets, transcribed into an excel sheets. The data were imported into and analyzed using statistical package for social sciences (SPSS) version 25 software (USA-Chicago by Norman H. Nie et al). Independent t-test was used for mean comparison, Fisher's exact test and Chi-square test used to compare proportions. A p-value <0.05 was considered for a significant statistical association between groups.

Ethical consideration
Each and every case was given a code during data collection and matching it with the histopathology case number. No patient's name appeared neither on data collection form nor during data presentation. The study was approved by the University of Rwanda College of Medicine and Health Sciences (UR-CMHS) Institutional Review Board (IRB), ethical approval number "No452/ CMHS IRB/2019".

Limitations of the study
We faced a challenge in staging all NHLs cases due to lack of clinico-radiological information in patients' files. Also, a probability of a low rate of detection of lymphomas in Rwanda because of culture and belief of some of the population.

RESULTS
This study included 306 cases of lymphomas. There was a predominance of male patients 174(56.8%), as shown in Table 1

DISCUSSION
This study shows that lymphomas affects predominantly male than female population in Rwanda; that trend is almost similar for both NHL and HL (P=.301). In comparison, these results are similar to those reported from Egypt 8 , Iran 9 and India. 10 A peak age of HL between 15 to 35 years noticed in this study was also previously reported in other settings. 11 However, there is lack of the second HL peak age in Rwanda, most likely due to the fact that there is a small number of the population above 65 years of age in Rwanda. 12 In our cohort, the rate of HIV positivity among lymphoma cases was 18%, which is quite higher than the prevalence (3%) of HIV positivity reported in the general population of Rwanda. 13 This finding was observed elsewhere. 14 The predominance 213(70%) of NHLs (versus HL) observed in this study was also documented in studies done in Iran (64.5%), Iraq (76%) and Southern India (78.7%). [15][16][17] Aggressive form of NHLs was over-represented in Rwanda compared to other settings. In accordance, while aggressive NHL represents 164(77%) of NHL in Rwanda, it is approximately 53% in Central and Southern America, 37% in Northern America and 36% in Poland. 18 Moreover, the aggressive form of NHL in Rwanda exhibits male predominance (81%) and the most affected age range was <15 years. Similar albeit weaker trend was seen in a study done in Iran witha male to female ratio of 1.8:1. 15 A possible predominance of paediatric forms of lymphoma (Burkitt and Burkitt-like, potentially misclassified) among aggressive NHL in Rwanda should be investigated using advanced methods as put forth in the current WHO classification; 19 such methods merit to be introduced in Rwanda.

CONCLUSIONS
As reported elsewhere, there is a male predominance and high rate of HIV positive cases among lymphoma patients in Rwanda. Lymphoma in Rwanda affects younger patients than in other regions. Interestingly, the most aggressive forms of NHL predominate in childhood, which may imply that these cases are Burkitt or Burkitt-like lymphomas. This assumption is to be verified through the introduction of genomic and other advanced diagnostic methods in Rwanda.