BRCA1 and pachyonychia congenita: The proportion of germline BRCA1 mutation carriers among patients with metastatic PC was available from 10 articles, for a total of 3963 patients, and was equal to 0.94% (95% CI: 0.19–2.23), with significant heterogeneity (I2 = 88.85%; p < 0.0001) (Figure 2c).