To the Editor, The aim of this letter is to describe our experience with the treatment of a nonresectable retroperitoneal lymph node with high-intensity focused ultrasound (HIFU). A 69-year-old woman developed a malignant tumor in the left breast in February 2006 and underwent quadrantectomy and sentinel lymph node excision at our institution. Pathological examination showed invasive mixed ductal and lobular carcinoma, and no invasion was seen in the adjacent blood vessels, lymphatics, or lymph nodes. The patient also has a past positive oncologic history for squamous cell carcinoma of the anal canal, which was treated with radical surgery and radiochemotherapy 2 years earlier, with no evidence of recurrence at the time of the quadrantectomy. After breast tumor excision, the patient received radiotherapy (21 Gy) and adjuvant hormonal therapy from May 2006 to February 2008. She remained free of disease until March 2008, when in a follow-up ultrasound (US) scan a single 30-mm hypoechoic solid mass was detected close to the hepatic hilum and was considered likely to be a metastatic lymph node. Multidetector computed tomography (MDCT) showed the presence of a large hilar hepatic node with inhomogeneous enhancement after contrast injection. It also excluded any other apparent site of disease. To characterize the finding, percutaneous US-guided core biopsy of the mass was performed using an 18 G needle. Pathology and immunohistochemistry confirmed the presence of metastatic cells from breast cancer. The surgical team did not consider the patient a suitable candidate for resection due to her history of cardiac failure and existing comorbidities. The lesion was also not considered suitable for percutaneous ablation due to the potential risk of thermal injury of the adjacent structures; therefore, observation of the lesion and continuation of chemotherapy with nonsteroid aromatase inhibitors was decided. Two months later (May 2009), the lesion showed growth of 1 cm on MDCT. The patient was re-evaluated in a multidisciplinary meeting comprising surgeons, oncologists, radiotherapists, and interventional radiologists. A consensus regarding the patient’s disease state was reached, thus leading to a new treatment plan. The patient was enrolled in a phase I study for HIFU treatment of solid tumors associated with chemotherapy using aromatase inhibitors. The patient had a Karnofsky performance scale score of 80%, with no contraindication to general anesthesia. The lesion was visualized before the procedure using US, and no gas interfered in the acoustic pathway. Informed consent was obtained. She was status NPO for 6 h before the procedure. The skin overlying the lesion was carefully shaved to avoid also any possible interference of hair in the acoustic pathway of HIFU, and a urinary catheter was inserted before treatment. General anesthesia was administered by the anesthetics team to achieve the patient’s complete immobilization and to prevent any pain. A purified-water balloon was used to push and compress bowel loops to avoid the presence of air G. Orgera (&) G. Bonomo L. Monfardini P. Della Vigna F. Orsi Unit of Interventional Radiology, European Institute of Oncology, Via Ripamonti 435, 20141 Milan, Italy e-mail: gianluigi.orgera@ieo.it