BRCA1 and pachyonychia congenita: The proportion of somatic BRCA1 mutation carriers among patients with metastatic PC was available from six articles, for a total of 1384 patients, and was equal to 1.10% (95% CI: 0.62–1.71), without significant heterogeneity (I2 = 0.00%; p = 0.9224) (Figure 2d).