About 25-50% of women with Cowden disease, a syndrome associated with germ-line mutations of the PTEN gene (at 10q23), develop breast cancer (BC), but PTEN mutations have been found in only 5% of sporadic BCs.
Additional genes, PTEN (Cowden disease), MSH1 or MLH2 (HNPCC), and p53 (Li-Fraumeni syndrome) are responsible for other breast cancer syndromes but have not yet entered the clinical arena on a large scale.
Additionally, germ-line mutations of PTEN/MMAC1 are responsible for several familial neoplastic disorders, including Cowden disease and Bannayan-Zonana syndrome.
Along with previous reports, this case suggests that acral plexiform PENs may be an early, highly specific finding in CS and highlights the importance of screening these patients for PTEN mutation.
Although CS is the only PHTS with a clearly documented predisposition to malignancies, pending further data, for precautionary reasons all individuals with a germline PTEN mutation are recommended to follow the cancer surveillance recommendations for CS.
Although a consensus cancer surveillance protocol has not been formally instituted, all PTEN mutation carriers should adopt the cancer surveillance strategies proposed for patients with Cowden syndrome.
An association of testicular malignancy in Cowden disease could be explained by the previous observation of strong PTEN gene expression in the basal cell layer around seminiferous tubules and increased frequency of PTEN mutations in cultured testicular cancer cell lines.
As PTEN is a dual phosphatase mutated in autosomal inherited disorders with phenotypes similar to those of PJS (Bannayan-Riley-Ruvalcaba syndrome and Cowden disease), our study suggests a functional link between the proteins involved in different hamartomatous polyposis syndromes and emphasizes the central role played by LKB1 as a tumor suppressor in the small intestine.
Because loss of PTEN can activate mTOR and mTOR inhibitors are Food and Drug Administration approved to treat renal cell carcinoma, these agents have clinical potential in renal cell carcinoma associated with Cowden syndrome.
Caveolin-1 is of particular functional interest because it has been shown to interact with PTEN, the tumor suppressor gene mutated in Cowden syndrome, an inherited multiple hamartoma syndrome that includes predisposition to FTC.