Seasonal Variation in Inflammatory Breast Cancer

Purpose: The epidemiologic characteristics of inflammatory breast cancer (IBC) suggest a strong environmental influence. Preliminary data from cluster studies have suggested that IBC may be precipitated by infectious agents or exposures to various chemicals. To investigate the infectious agent hypothesis we looked for seasonal variation in onset of IBC. Methods: We compared the IBC incidences in Canada and the states in the United States with cold winter temperatures to IBC incidences in states with milder winter temperatures. The IBC cases were characterized by the state they lived in and season, when diagnosed. Results: Of the 306 IBC cases that were evaluable, the average number of cases per month in the winter was 20.3, compared to 27.2 diagnosed in the rest of the year. Of the 203 cases in the cold winter group, the average number in winter months was 13 vs. 18.2 for the non-winter months. In the other group of 103 patients, the average number in winter was 7.3 vs. 9 in the non-winter months. The percentage of cases diagnosed in winter in the cold winter group was lower than in the high winter group.