Dear Editor, Hereditary hemorrhagic telangiectasia (HHT, Rendu–Osler– Weber syndrome) is an inherited vascular dysplasia. Typical signs are mucocutaneous telangiectases, epistaxis, gastrointestinal bleeding, anemia, and problems due to large visceral vascular shunts [1]. Little is known about the underlying molecular pathogenetic mechanism; however, unbalanced angiogenesis involving the transforming growth factor-β and vascular endothelial growth factor (VEGF) signaling pathways has been assumed [1]. Phosphoinositide 3-kinase (PI3K) signaling plays an important role in the vascular system via VEGF signaling [2]. Here, we report about a patient with HHT who showed an impressive response during treatment with the pan-class I PI3K inhibitor BKM120. Informed consent was obtained from the patient for publication of this observation. The submission of the manuscript has been approved by the institutional review board (“Studienkommission”) of the Hospitals of the City of Cologne. A 49-year-old woman had a positive family history for HHT, long-standing epistaxis, mucocutaneous telangiectases, and anemia. Genetic testing revealed a frameshift mutation in the Activin receptor-like kinase-1 gene (HHT2). In April 2009, a stage IV serous–papillary ovarian cancer was diagnosed. She received surgery and several lines of chemotherapy containing carboplatin, cisplatin, paclitaxel, and namitecan (a camptothecin derivative) until September 2011. Up to this date, epistaxis had been quite stable for several years, occurring several times a day (Table 1) and was unaffected by these therapies. From November 2011 to March 2012, the patient received treatment as part of a phase I trial consisting of four cycles of weekly paclitaxel (80 mg/m iv; days 1, 8, 15, 22; q28 days) and continuous daily BKM120 (100 mg flat dose orally). After the first treatment with BKM120, the patient noted a dramatic decrease in the frequency of epistaxis, which then completely stopped after 6 weeks of therapy. When the ovarian cancer progressed, the patient was switched to a treatment with epirubicin and pazopanib from April 2012 to June 2012. In July 2012, approximately 4 months after the last dose of BKM120 was given, the patient began to experience infrequent mild bleeding from her nose again (Table 1). The bleeding was often initiated by digital manipulation when cleaning the nose, and it did not seem to progress over time. Hemoglobin levels are not discussed in this report as there are many confounding parameters such as chemotherapy, intravenous iron substitution, uncertainty about gastrointestinal involvement, and rare transfusions. U. W. Geisthoff (*) Department of Otorhinolaryngology, Holweide Hospital, Hospitals of the City of Cologne, Cologne, Germany e-mail: geisthoffu@kliniken-koeln.de URL: www.geisthoff.de