Garcia et al. evaluated the mammary histomorphology of 19 postpubertal women with CF [
7]. They reported two cases of an invasive mammary carcinoma, ductal type, low grade and one case of an invasive ductal type of high grade. Previous epidemiologic studies have demonstrated a low incidence of breast cancer. A study of cancer risk among patients with CF in North American countries was conducted between 1985 and 1992 and compared with European registeries. The authors reported 41 cases of tumor, with only 2 cases of breast carcinoma, while in Europe there was no case of breast cancer in the overall 41 tumor cases [
8]. The number of reported cases was compared to the number of expected cases (calculated from population-based data on cancer incidence) and breast cancer had a low observed-to-expected ratio (0.8) [
8]. Most of the cases manifested over 30 years of age. In an other study with more than 40,000 CF patients, 172 cases of cancer were reported between 1990 and 2009 [
9]. The authors reported a declining incidence trend in the second decade of the study period compared to the first decade (standardized incidence ratio 0.7, CI 95%) [
9]. In contrary, Archangelidi et al. reported opposite trends in cancer epidemiology. The authors compared data from the CF registry in UK with data from the general population between 1999 and 2017 [
3]. As a result, 146 cases of malignancy were identified, of these, 13 cases of breast cancer. This means a rate of 46.5/100,000 cases (95%, CI: 33-59.8) in the CF population vs. 14.5/100,000 in the general population. The results of this study should be interpreted with precaution due to the small number of patients. No increased risk was seen in association with homozygosity for
F508del mutation. The fact that heterozygosity for CF gene is not a risk factor for breast cancer was also confirmed in a Swedish study where CF patients and their closest relatives were followed [
10]. However, this study didn’t record any case of breast cancer. In the Austrian CF center between 1995 and 2019, they recorded 11 cases of malignant disease in 229 patients [
11]. Although they did not record any cases of breast cancer, it is interesting that of these 11 cancer patients, 10 were women. Despite the number of patients with breast cancer was small, a trend towards increasing incidence could be seen over time (Table
1).