[Leukemias and other hemoblastoses: description of unusual clustering and difficulties in evaluation. A report on the epidemiology of leukemias and related diseases in rural communities].

The purpose of this study, drawn up as a localised report, was to find out whether the accumulation of notified cases of leukaemia and haemoblastosis over a 40-year observation period, in a restricted region within a small village, can also be found in other localities of the northern Bavarian administration district of Kronach. This region was very out-of-the-way before German reunification. With its static indigenous population, and the retrieval possibilities of respective archives, it offered good conditions for a long-term study over four decades; 13 out of 63 administrative district communities could be randomly selected for research. Between 1950 and 1993, 144 patients who contracted either leukaemia or another type of malignant neoplasm of the lymphoid and haematopoetic tissues were recorded (Pos. C 81-C 96 ICD 10). When these patients' dwellings were charted, a sporadic, inconspicious, temporal-spatial distribution became apparent in seven out of 13 localities. However, in six of the 13 communities there was the same limited local concentration of cases spread over a period of time, as had been observed in the abovementioned village. This cartographically noticeable concentration was termed "cluster"; in these "clusters", both locals and long-term residents were affected. What these "clusters" have in common topographically is that they are noticeably located in moist areas. The study clearly demonstrates the difficulties in assessing these cartographically significant "clusters" from a statistical point of view, i.e. in making a risk quantification for small populations and with insufficient demographic data. Therefore, no statement can be made as to whether the observed "clusters" represent change findings, or rather, an epidemiological, i.e. endemic fundamental pattern of leukaemia and haemoblastoses; one that, within a shorter observation period, must remain undetected-that is, could be disguised by population migrations.