PTEN Hamartoma Tumour Syndrome: Germline PTEN Loss

One Gene, Several Named Syndromes

PHTS covers Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome and other presentations that share a germline PTEN pathogenic variant. Grouping them by gene rather than by clinical label reflects that they are one molecular entity with variable expression.

Features can differ markedly between people, even within the same family, and can be subtle before any cancer develops.

Why Losing One PTEN Copy Matters

PTEN is dose-sensitive: even a partial reduction in PTEN function raises PI3K-AKT-mTOR signalling. A person with a germline pathogenic variant starts with reduced PTEN in every cell, so a single further somatic hit can fully deregulate the pathway in a tissue.

This is the same two-hit logic seen with other inherited tumour-suppressor conditions.

Associated Cancer Risks

PHTS is associated with increased lifetime risks of breast, thyroid (typically follicular or papillary), endometrial and renal cancers, and of colorectal polyps and cancer. Reported risk estimates vary between studies and cohorts.

Because estimates are population summaries, an individual's risk discussion depends on personal and family history and is handled through a genetics service.

Benign and Developmental Features

Common non-cancer features include macrocephaly, characteristic skin findings such as trichilemmomas and oral papillomas, gastrointestinal hamartomas, thyroid nodules and vascular anomalies.

Some individuals have neurodevelopmental effects ranging from none to autism spectrum disorder, and a proportion of cases arise from a new (de novo) variant rather than an inherited one.

Interpretation Notes

A tumour that shows somatic PTEN loss does not indicate PHTS; the syndrome is defined by a germline pathogenic variant confirmed on constitutional DNA.

A PTEN variant of uncertain significance is not a diagnosis, and reclassification over time is handled by the testing laboratory and genetics team.

Key Takeaways

• ·PHTS is caused by germline pathogenic PTEN variants and includes Cowden syndrome.
• ·PTEN is dose-sensitive, so one inherited hit primes the PI3K pathway for deregulation.
• ·Associated cancers include breast, thyroid, endometrial and renal, with variable risk estimates.
• ·Somatic PTEN loss in a tumour does not establish PHTS; a germline test does.