Robust Anti-tumor Response in a Patient with Metastatic Gastroesophageal Junction Adenocarcinoma on Long-term Maintenance Chemotherapy With Trastuzumab Alone: An Unusual Occurrence

Esophageal adenocarcinoma arises after a normal squamous mucosa undergoes metaplasia to the specialized columnar epithelium, which can then ultimately progress to dysplasia and subsequent malignancy. It typically presents at an advanced stage, and despite optimal management, the prognosis remains poor. Recently, the ToGA (Trastuzumab for Gastric Cancer) trial evaluated the role of trastuzumab (Herceptin®) in human epidermal growth factor receptor 2 (HER2) over-expressing gastric and gastroesophageal junction (GEJ) adenocarcinoma and showed improvement in overall survival when trastuzumab was added to the standard chemotherapy compared to standard chemotherapy without trastuzumab. However, data and experience are lacking in the literature regarding the use of trastuzumab outside of combination chemotherapy. The optimal length and safety of trastuzumab use as maintenance therapy in the long-term are also unclear in patients with gastric or GEJ adenocarcinomas after sustained remission. We report a case of metastatic GEJ adenocarcinoma, where the patient first showed an exceptional response to standard chemotherapy combined with trastuzumab and subsequently could sustain a long-lasting remission on maintenance therapy with trastuzumab alone. Trastuzumab was ultimately discontinued owing to the lack of clear knowledge regarding its length and safety of use as maintenance therapy in the long-term.