Contributions
Type: Publication Only
Background
Chronic Lymphocytic Leukemia (CLL) is the most common type of leukemia diagnosed in the Western world. The causes of its occurrence remain unclear: environmental factors are involved, such as farming related and chemical exposures. Family history of any hematological malignancy may also increase risk of CLL. Reunion Island is an 874.000 inhabitants tropical French overseas department located in the southwestern Indian Ocean. Because of its insularity and the significant interbreeding population, this territory lends itself to genetic peculiarities. The fraction of people of each ethnicity is not known exactly. A 2002 regional report estimated the distribution of different ethnic groups as 33% Persons of mixed race, 27% Caucasians, 20% Indians, 17% Africans and 3% Chinese.
Aims
In the absence of previous epidemiological study, we conducted a comprehensive review of epidemiological, prognostic and therapeutic characteristics of CLL Reunionese patients over a period of ten years, between 2004 and 2013.
Methods
Inclusion criteria were as follows: any French patient having a permanent residence on Reunion Island and matching the NCI/WG diagnosis criteria for the 2004-2008 period, or the IWCLL diagnosis criteria for the 2009-2013 period. Monoclonal B-cell lymphocytosis as well as small lymphocytic lymphomas were not included in the study. Variables analyzed were age at diagnosis of CLL, sex, prognostic markers (ZAP-70, lymphocyte doubling time, B2-microglobulin, and where available del (17p13)), stage at diagnosis and treatment intervention.
Results
A total of 134 cases of CLL were identified in this study. The age-standardized incidence rate was 1.23 per 100.000 with a male/female sex ratio of 1.98:1. Median age at diagnosis is 63 (range, 38-93 years). 37.3% of patients were under 60 years. A majority of CLL diagnosis (86.3%) were discovered incidentally after a blood cell count is performed for another reason. More patients were at early stage (Binet A) versus advanced (Binet B or C) at the time of CLL diagnosis (77% versus 23%). Median absolute lymphocyte count at diagnosis was 11.7 G/L. When treatment was indicated (30%), 2/3 patients (12%) received immunochemotherapy as first-line treatment. The median time to treatment was 21.9 months. The overall survival at 5 years is 85%.
Summary
All CLL diagnosis in Reunion Island are carried out a priori in one of the two Hospital Centers existing on the island, which are the only facilities able to perform blood lymphocytic immunophenotyping by flow cytometry. The French National Network of Registers FRANCIM analyses together CLL and small lymphocytic leukemia: the 2012 incidence rate on the whole French territory is estimated at 4.4 and 2.2, in men and women respectively, per 100,000. CLL incidence seems twice to three times lower on Reunion Island. Despite a comparison bias between national and Reunionese statistics, the difference appears significate. This Reunionese peculiarity might be explained either by genetic factors related to a highly mixed population, or by environmental factors. Another hypothesis which might explain the low CLL incidence would be an under-use of public and private medical facilities by the Reunionese, in particular elderly people. Besides, sharing between Binet classification stages is the same as the one reported in the literature. No significant differences were identified in overall survival compared with European CLL patients. The low CLL incidence observed on Reunion Island is probably due to multiple factors and requires further investigations. The determination of each patient’s ethnic origin shall highlight a possible under-representation of one or several population categories.
Keyword(s): Chronic lymphocytic leukemia, Epidemiology
Type: Publication Only
Background
Chronic Lymphocytic Leukemia (CLL) is the most common type of leukemia diagnosed in the Western world. The causes of its occurrence remain unclear: environmental factors are involved, such as farming related and chemical exposures. Family history of any hematological malignancy may also increase risk of CLL. Reunion Island is an 874.000 inhabitants tropical French overseas department located in the southwestern Indian Ocean. Because of its insularity and the significant interbreeding population, this territory lends itself to genetic peculiarities. The fraction of people of each ethnicity is not known exactly. A 2002 regional report estimated the distribution of different ethnic groups as 33% Persons of mixed race, 27% Caucasians, 20% Indians, 17% Africans and 3% Chinese.
Aims
In the absence of previous epidemiological study, we conducted a comprehensive review of epidemiological, prognostic and therapeutic characteristics of CLL Reunionese patients over a period of ten years, between 2004 and 2013.
Methods
Inclusion criteria were as follows: any French patient having a permanent residence on Reunion Island and matching the NCI/WG diagnosis criteria for the 2004-2008 period, or the IWCLL diagnosis criteria for the 2009-2013 period. Monoclonal B-cell lymphocytosis as well as small lymphocytic lymphomas were not included in the study. Variables analyzed were age at diagnosis of CLL, sex, prognostic markers (ZAP-70, lymphocyte doubling time, B2-microglobulin, and where available del (17p13)), stage at diagnosis and treatment intervention.
Results
A total of 134 cases of CLL were identified in this study. The age-standardized incidence rate was 1.23 per 100.000 with a male/female sex ratio of 1.98:1. Median age at diagnosis is 63 (range, 38-93 years). 37.3% of patients were under 60 years. A majority of CLL diagnosis (86.3%) were discovered incidentally after a blood cell count is performed for another reason. More patients were at early stage (Binet A) versus advanced (Binet B or C) at the time of CLL diagnosis (77% versus 23%). Median absolute lymphocyte count at diagnosis was 11.7 G/L. When treatment was indicated (30%), 2/3 patients (12%) received immunochemotherapy as first-line treatment. The median time to treatment was 21.9 months. The overall survival at 5 years is 85%.
Summary
All CLL diagnosis in Reunion Island are carried out a priori in one of the two Hospital Centers existing on the island, which are the only facilities able to perform blood lymphocytic immunophenotyping by flow cytometry. The French National Network of Registers FRANCIM analyses together CLL and small lymphocytic leukemia: the 2012 incidence rate on the whole French territory is estimated at 4.4 and 2.2, in men and women respectively, per 100,000. CLL incidence seems twice to three times lower on Reunion Island. Despite a comparison bias between national and Reunionese statistics, the difference appears significate. This Reunionese peculiarity might be explained either by genetic factors related to a highly mixed population, or by environmental factors. Another hypothesis which might explain the low CLL incidence would be an under-use of public and private medical facilities by the Reunionese, in particular elderly people. Besides, sharing between Binet classification stages is the same as the one reported in the literature. No significant differences were identified in overall survival compared with European CLL patients. The low CLL incidence observed on Reunion Island is probably due to multiple factors and requires further investigations. The determination of each patient’s ethnic origin shall highlight a possible under-representation of one or several population categories.
Keyword(s): Chronic lymphocytic leukemia, Epidemiology