• Hironori Arai, Kiwamu Akagi, Ayako Nakagawa, Yasuhide Onai, Yoshikazu Utsu, Shinichi Masuda, and Nobuyuki Aotsuka.
• Department of Hematology and Oncology, Japanese Red Cross Narita Hospital, Narita, Japan.
• Medicine (Baltimore). 2023 Jan 6; 102 (1): e32572e32572.

IntroductionCowden syndrome is a rare autosomal dominant disease characterized by the development of hamartomas and increased risks of other tumors, including breast, thyroid, and uterine cancers. Most patients with Cowden syndrome show mutations of the phosphatase and tensin homolog (PTEN) gene on chromosome 10; however, some patients with mutations do not show clinical symptoms, while patients with clinical symptoms may not have detectable PTEN mutations.Case PresentationA 39-year-old woman with macrocephaly had previously been diagnosed with Cowden syndrome at another hospital, when she presented with the onset of breast cancer. A wide variety of complications were detected, including cerebellar tumors treated by resection, hydrocephalus, and multiple polyps in the stomach and large intestine. She was further diagnosed with adult-onset Lhermitte-Duclos disease as a complication of Cowden syndrome. She subsequently developed a dural arteriovenous fistula treated by transvenous embolization. After transfer to our hospital, she developed adenomatous goiter treated by resection, recurrent breast cancer treated with hormonal therapy, and multifocal oral mucosal papillomatosis. Her older sister had previously been diagnosed with Cowden syndrome and her father was undiagnosed but had macrocephaly, hydrocephalus, and multifocal oral mucosal papillomatosis, suggestive of Cowden syndrome. After consultation with a genetic specialist, analysis of the PTEN gene showed a rare but likely pathogenic germline c.801 + 2T>A variant located at the splice donor site of intron 7. The patient's clinical diagnosis of Cowden syndrome was accordingly confirmed by the genetic findings. Appropriate surveillance procedures were put in place to detect any further tumors.ConclusionsThe clinical symptoms of Cowden syndrome do not always correlate with the genetic results. However, recent improvements in genetic testing suggest the importance of diagnosing this disease using both clinical and genetic approaches, in collaboration with genetic experts, to ensure an accurate diagnosis and appropriate surveillance for malignant tumors.Copyright © 2022 the Author(s). Published by Wolters Kluwer Health, Inc.

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