Cowden syndrome is a rare genetic condition that causes noncancerous growths called hamartomas to develop throughout the body, along with a significantly elevated lifetime risk of several cancers. It affects roughly 1 in 200,000 people. The syndrome is caused by a mutation in a single gene that normally keeps cell growth in check, and it’s inherited in a pattern where only one copy of the faulty gene is enough to cause problems.
What Causes Cowden Syndrome
Cowden syndrome results from a mutation in the PTEN gene, which acts as a tumor suppressor. In a healthy cell, the protein made by this gene puts the brakes on a signaling pathway that tells cells to grow and survive. When PTEN is working properly, it keeps cell division at a controlled pace and allows damaged cells to die off naturally.
In people with Cowden syndrome, one copy of the PTEN gene is already mutated from birth. When the remaining working copy gets damaged over time (a process geneticists call a “second hit”), the cell loses its growth brakes entirely. The result is an overgrowth of tissue that forms hamartomas, benign masses made of normal cell types that have simply piled up in the wrong place or in excessive amounts. These growths can appear on the skin, in the digestive tract, in the thyroid, the uterus, and the brain.
The condition follows an autosomal dominant inheritance pattern. If one parent carries the mutation, each child has a 50% chance of inheriting it. Some cases, however, arise from brand-new mutations in people with no family history of the disorder.
Skin and Mouth Changes
The earliest and most visible signs of Cowden syndrome are skin lesions, which appear in 90% to 100% of affected individuals. They typically show up in a person’s twenties or thirties. The hallmark growths are trichilemmomas, small flesh-colored bumps that develop around the face, especially near the hairline, nose, and mouth. Individually, they look unremarkable, but having multiple ones is a strong clue.
Other common skin findings include small pits or thickened bumps on the palms of the hands and soles of the feet (acral keratoses), small nerve-related growths on the skin or mucous membranes, and papillomas (wart-like bumps) on the gums and tongue. Having three or more of any of these types of lesions is considered a major diagnostic criterion. Many people live with these skin changes for years before anyone connects them to an underlying syndrome, since each individual bump can look harmless on its own.
Cancer Risks
The most serious consequence of Cowden syndrome is a dramatically increased lifetime risk of cancer. A large longitudinal study published in JAMA Network Open found the following lifetime cancer risks for people with PTEN mutations:
- Breast cancer: 91%
- Endometrial cancer: 48%
- Thyroid cancer: 33%
- Kidney cancer: 30%
- Melanoma: 5%
The breast cancer risk alone is higher than what’s seen with BRCA mutations, which makes Cowden syndrome one of the highest-risk hereditary cancer syndromes known. Thyroid cancers in Cowden syndrome tend to be follicular carcinomas, a less common subtype than what’s typically seen in the general population. Colorectal cancer risk is also elevated, though exact lifetime figures vary across studies.
Digestive Tract Involvement
Polyps throughout the gastrointestinal tract are common. In one study of Cowden syndrome patients who underwent colonoscopy, 95% had inflammatory (juvenile-type) polyps, 63% had lymphoid follicle polyps, and 53% had ganglioneuromatous polyps. These are generally benign, but they don’t tell the whole story. More than half the patients in the same study also had colonic adenomas, the type of polyp that can progress to cancer, and 11% had already developed colorectal adenocarcinoma. This combination of benign overgrowth and genuine cancer risk is what makes ongoing surveillance so important.
Other Features
A larger-than-average head (macrocephaly) is one of the most consistent physical features. In adults, this means a head circumference above the 97th percentile: greater than 58 cm in women or 60 cm in men. In children with PTEN mutations, macrocephaly is almost universal and often dramatic, averaging around 5 standard deviations above the mean.
Developmental differences can also be part of the picture. Autism spectrum disorder and intellectual disability are listed among the minor diagnostic criteria. Research suggests that 10% to 20% of people who have both autism and macrocephaly carry a PTEN mutation, even if they don’t have other obvious signs of Cowden syndrome. Benign thyroid growths, fatty tumors (lipomas), and vascular anomalies round out the list of associated features.
How It’s Diagnosed
Diagnosis uses a combination of clinical findings and genetic testing. The clinical criteria, developed by the National Comprehensive Cancer Network, include 8 major and 10 minor criteria. Major criteria include breast cancer, endometrial cancer, follicular thyroid carcinoma, multiple gastrointestinal hamartomas, macrocephaly, and the characteristic mucocutaneous lesions described above. Minor criteria include colorectal cancer, kidney cancer, lipomas, thyroid structural lesions, and autism spectrum disorder.
A clinical diagnosis is established when a person meets three or more major criteria (one of which must be macrocephaly, a specific cerebellar tumor called Lhermitte-Duclos disease, or gastrointestinal malrotation), or two major criteria plus three minor criteria. For family members of someone already diagnosed, the threshold is lower: two major criteria, or one major and two minor criteria. Genetic testing for a PTEN mutation can confirm the diagnosis and is especially useful for family screening. For children, the threshold for testing is deliberately low. Macrocephaly plus just one other feature is enough to warrant genetic evaluation.
Related Conditions on the PTEN Spectrum
Cowden syndrome isn’t the only condition caused by PTEN mutations. It belongs to a family of disorders collectively called PTEN hamartoma tumor syndrome (PHTS). This spectrum also includes Bannayan-Riley-Ruvalcaba syndrome, which typically presents in childhood with macrocephaly, intestinal polyps, lipomas, and freckling on the genitalia. PTEN-related Proteus syndrome and Proteus-like syndrome, which cause asymmetric overgrowth of bones, skin, and other tissues, are also part of the spectrum. Different people with the same PTEN mutation can end up with very different clinical presentations, which is one reason these conditions were historically considered separate diseases before their shared genetic basis was understood.
Living With Cowden Syndrome
Because Cowden syndrome can’t be cured, management centers on early detection of cancers through a structured screening schedule that begins earlier and repeats more frequently than screening for the general population. This typically means annual breast MRIs and mammograms starting in early adulthood, regular thyroid ultrasounds, periodic colonoscopies, and endometrial screening for women. Some individuals with very high breast cancer risk choose preventive mastectomy, and preventive hysterectomy may be discussed after childbearing is complete.
The skin growths themselves are benign and are usually managed cosmetically if they’re bothersome. Gastrointestinal polyps may need periodic removal during colonoscopy, particularly if adenomas are found. Because the condition is inherited, genetic counseling is an important step for anyone diagnosed, both to inform their own relatives and to understand the implications for future children.