Gastric cancer continues to be the fifth most common malignancy worldwide and the third leading cause of cancer-related death in both sexes.

Despite recent progress in the development of new therapeutic strategies, prognosis in advanced gastric cancer continues to be poor.

Therefore, determining the prognostic factors that can help identify patients who would derive little survival benefit from current therapeutic strategies and who should be actively recruited into clinical trials evaluating alternative treatment approaches becomes of paramount importance.

In recent years, several prognostic scores based on clinical and laboratory attributes have proven to predict survival in large cohorts of metastatic gastric cancer patients undergoing first-line palliative chemotherapy.

The two most commonly used indices developed on the basis of large patient cohorts are the Royal Marsden Hospital prognostic index (RMH-I) and the Japan Clinical Oncology Group prognostic index (JCOG-I) for Caucasian and Asian populations, respectively.Both models were derived and validated using data from subjects enrolled in multicenter, phase III clinical trials. However, this population extracted under the ideal inclusion criteria of regulatory trials may not be representative of patients cared for in everyday clinical practice, who tend to be older, have worse functional status, as well as acute and chronic comorbidities. Consequently, it is likely that some important prognostic variables may not have been adequately contemplated and it would be convenient to know what the prognostic impact of this is in the real world. Furthermore, some of the aforementioned scores were elaborated prior to HER2 testing and front-line trastuzumab for HER2-positive tumors became standard in clinical practice and none have assessed their potential impact on prognosis.

To our knowledge, the AGAMENON-derived nomogram is the first one developed and validated on the basis of data from a Caucasian population in daily clinical practice, in which the prognostic impact of HER2 status and trastuzumab therapy was evaluated and found to predict survival. It has demonstrated its superior performance in comparison with the RMH-I and the JCOG-I in this setting. The results of our research are mainly applicable in assisting clinicians in risk stratification and to support individualized, clinical decision-making in actual series of unselected patients with advanced gastric cancer in routine clinical practice. It can also be used both for patient selection and accurate baseline stratification in the design of forthcoming clinical trials.