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Dear editor,

We were interested in the letter of Bouchardy et al. concerning myeloid leukemia in French Polynesia.1 It was important to report the abnormally high incidence of this rare disease. The Hôtel-Dieu hospital in Paris has an agreement with the French Polynesian government to organize clinical, epidemiological and scientific support for patients suffering from hematological conditions. Our collaboration started in May 1985 and is still continuing. The large number of leukemias led us to work with F. De Vathaire1 to analyze the epidemiology of these conditions. All patients diagnosed with malignant hematological conditions were referred to our staff by internists or a hematologist (LH) present in Papeete (French Polynesia) where the territorial hospital is situated and where patients from the five archipelagos are treated. Data collection was established with the registration of all cases and confirmation of the diagnosis of cases was provided by local public and private biology laboratories. Records were cross-checked with the medical sanitary transfer to metropole files of the public health office. All slides were reviewed in our university hospital in Hôtel-Dieu, Paris. Epidemiological analysis was performed by four 4-year periods for the period 1986 to the end of 2001. Because the distribution of leukemia types in Polynesian Maori of New Zealand and Hawaian native populations are known to be different from that observed in other parts of the world,2 we considered only the native population of French Polynesia. Leukemia was classified according to the ICD9 classification.

Incidence was truncated to adults more than 15-year old because of doubtful complete registration of childhood cases, who could have been directed to New Zealand, USA or France without the diagnosis being established locally.

Due to the size of both the French Polynesian and the reference population and the small number of cases, internal and external comparisons were performed using Fisher's exact test or chi-square tests stratified by age class. The power of the geographical comparisons has been estimated assuming that the number of leukemia cases followed a Poisson distribution.3

In total 101 patients presented with leukemia. The age-standardized incidence rate to the World population [ASR(W)] of all leukemia was 6.2/100,000py (6.9 in men and 5.6 in women) with an unusual distribution of sub-types due to a very low incidence of chronic lymphoid leukemia (Table 1). The ASR(W) of acute myeloid leukemia (AML) was 4.2/100,000py, 4.3 in men and 4.2 in women for the whole period. However, we identified a significant difference between the first and the last 8-year periods due to an absence of AML in patients above 65 years until 1994. This could be explained by a former low interest to define the cause of death in the elderly due to cultural features or difficulty in access to health care. French Polynesian health politics were modified in 1994 and new laws (“délibération n°94-6AT du 3 février 1994 définissant le cadre de la couverture sociale généralisée”) increased accessibility to care. Satellite phones were installed in the more distant islands. A network for medical evacuation—particularly increasing the number of airports in the five archipelagos—was developed at the same time. The development of the country, particularly the role of media in the provision of medical information increased the demand for care in parallel. These improvements could not modify the previous incidence but information about the elderly were more easily obtained in recent years. As a result the recorded incidence of AML increased from less <3 to 5.95/100,000py, which represents the highest recorded level in the world.

Table 1. Leukemias reported in French Polynesia between 1986/01/01 and 2001/12/31
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AML was significantly more frequent in natives of the Marquesas (6.9/100,000py, 95% CI: 2.1–11.8) than in natives of other archipelagos (4.0/100,000py, 95% CI: 2.9–5.0). The standardized incidence rate (SIR) for patients born in the Marquesas islands was significantly different from the SIR for patients originating from other archipelagos (p = 0.05; OR: 2.1; 95% CI: 1.01–4.39). Thus, although in this study, we analyzed small populations, we observed a significantly high rate of AML in the Marquesas islands.

All leukemia incidence was found to be similar to that observed in Hawaii during the same time period. When comparing incidence for the various types of leukemia, CLL incidence was found to be lower in French Polynesia than in Hawaii, both among women (p = 0.02) and men (p = 0.01). These data could suggest a less frequent use of medical check up, (the most frequent way to diagnose CLL), in French Polynesia.

Genetic susceptibility cannot be excluded as an explanation for the high rates of AML in the Marquesas islands but in association with the highest incidence of thyroid cancer in the world the hypothesis that these excess incidence rates are due to the “health consequences of exposure to radiations emanating from nuclear tests” as suggested by Bouchardy et al.1 cannot be dismissed.

References

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  • 1
    Bouchardy C, Benhamou S, de Vathaire F, Schaffar R, Rapiti E. Incidence rates of thyroid cancer and myeloid leukaemia in French Polynesia. Int J Cancer 2011; 128: 22413.
  • 2
    Curado MP, Edwards B, Shin HR, Storm H, Ferlay J, Heanue M, Boyle P. Cancer incidence in five continents, vol. IX. IARC scientific Publications no 160. Lyon: International Agency for Research on Cancer, 2007.
  • 3
    Breslow NE, Day NE. Statistical methods in cancer research, vol 2. The design and analysis of cohort studies. Lyon: International Agency for Research on Cance, 1987.

Bernard Rio*, Laurence Heuberger†, Gilles Soubiran†, Robert Zittoun*, Jean-Pierre Marie*, * Département d'hématologie, Hôtel-Dieu, Paris, France, † Service de médecine et unité d'hématologie, Centre Hospitalier de Polynésie Française, Papeete, Polynésie Française.