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Targeted therapies against HER2 (trastuzumab, lapatinib) have improved the efficacy of treatment and the outcome of patients with HER2-positive breast cancer. Lapatinib is a tyrosine kinase inhibitor targeting EGFR1 and HER2: it binds the intracellular domain of these receptors and blocks their downstream signaling pathways. In combination with capecitabine, it is the standard of care for patients with trastuzumab-resistant advanced breast cancer. We present the case of a patient exhibiting a complete and prolonged clinical response to second-line treatment with lapatinib and capecitabine after failure of trastuzumab-based therapy. 18FDG-PET allowed the detection of disease remission several months before computed tomography. Molecular imaging with 18FDG seems the most powerful way to measure the pharmacodynamic effects of targeted anticancer drugs. This case report confirms that18FDG-PET plays a key role not only in detecting metastatic disease but also in evaluating the response to HER2-directed therapy.

Background Metastases from breast cancer cause the frequent involvement of lung, bone, liver, and brain, while the occurrence of metastases to the gastrointestinal tract is rare, and more frequently discovered after a primary diagnosis of breast cancer. Solitary pancreatic metastases from breast cancer, without widespread disease, are actually unusual, and only 19 cases have been previously described; truly exceptional is a solitary pancreatic metastasis becoming evident together with the primary breast cancer. Case presentation A 68-year-old woman reported general fatigue, lethargy, and jaundice. Abdominal ultrasound (US) and magnetic resonance imaging (MRI) showed an ampulloma of Vater’s papilla; moreover, a neoplastic nodule in the left breast was diagnosed. She underwent surgery for both breast cancer and ampulloma of Vater’s papilla. Pathological examination of pancreatic specimen, however, did not confirm primary carcinoma of the duodenal papilla, but showed a metastatic involvement of pancreas from lobular breast cancer. Immunohistochemistry has been essential to confirm the origin of the malignancy: hormone receptors and mammaglobin were expressed in both the primary breast tumor and the pancreatic metastasis. Conclusions This is one of the few reported cases in literature of an isolated and synchronous pancreatic metastasis from breast cancer, where the definitive diagnosis was obtained only after surgery. We discuss the controversies in this diagnosis and the choice of correct treatment. The surgical resection of solitary metastases can be performed in the absence of disseminated disease.