On one hand, somatic mutations in SAMHD1 have been linked to several human cancers, being recurrently mutated in chronic lymphocytic leukemia (CLL) [6,7], frequently mutated in colorectal cancer [8], and other mutations have been found in a number of different cancers, including myeloma [9], breast cancer [10], lung carcinoma [11], pancreatic cancer [12], and glioblastoma [13]; overall suggesting that SAMHD1 may function as a tumor suppressor. Here, SAMHD1 is linked to breast cancer.