According to Genetics Home Reference website:
Cowden syndrome is a rare disorder characterized by multiple noncancerous, tumor-like growths called hamartomas and an increased risk of developing certain cancers.
Almost everyone with Cowden syndrome develops hamartomas. These growths are most commonly found on the skin and mucous membranes (such as the lining of the mouth and nose), but can also occur in the intestinal tract and other parts of the body. Abnormal growths on the skin and mucous membranes typically appear by a person's late twenties.
People with Cowden syndrome have an increased risk of developing several types of cancer, including cancers of the breast, thyroid, and the lining of the uterus (the endometrium). Noncancerous breast and thyroid diseases are also common. Other signs and symptoms of Cowden syndrome can include an enlarged head (macrocephaly); a rare, noncancerous brain tumor called Lhermitte-Duclos disease; and intellectual disability.
How common is Cowden syndrome?
Researchers estimate that Cowden syndrome affects about 1 in 200,000 people; however, the exact prevalence of this condition is unknown because it can be difficult to diagnose.
It’s the increased risk of cancers in the breast that was the focus of the Journal of Plastic, Reconstructive & Aesthetic Surgery article. It was for this reason that their 3 case report patients had prophylactic mastectomies with reconstruction.
According to the eMedicine article:
Carcinoma of the breast occurs in 20-36% of female patients and is one of the most serious consequences of Cowden disease (multiple hamartoma syndrome). Carcinoma of the breast also has been reported in 2 men with Cowden disease (multiple hamartoma syndrome). Fibrocystic disease and fibroadenomas are present in approximately 75% of patients.
And from the University of Iowa patient guide:
Of all the women diagnosed with CS, 30 to 50 percent of patients will develop breast cancer and 50 to 70 percent of patients will not develop breast cancer. The average age of breast cancer in women with CS is 38 years; however, cancer has been reported in patients ranging from 14 to 65 years of age. Women are also at increased risk for other benign breast conditions, such as ductal hyperplasia, intraductal papillomatosis, lobular hypertrophy, fibrocystic breast disease, or fibroadenomas.
Although the risks are lower, men with CS also have an increased risk for developing breast cancer. However, the degree of risk for breast cancer in men is unknown.
Cowden syndrome and reconstructive breast surgery: Case reports and review of the literature; E. Ali, P.G. Athanasopoulos, P. Forouhi, C.M. Malata; Journal of Plastic, Reconstructive & Aesthetic Surgery - 07 June 2010 (10.1016/j.bjps.2010.04.047)
Cowen Syndrome – Genetics Home Reference, A service of the U.S. National Library of Medicine®
Cowden Disease (Multiple Hamartoma Syndrome); eMedicine article, April 26, 2010; Kendall Adkisson, MD, Katherine H Fiala, MD
Cowden Syndrome: A Guide for patients and their families; April 2002; University of Iowa Hospitals and Clinics