In this study, the incidence of GC with AM steadily increased over the past 16 years to approximately 0.1 per 100,000. To our knowledge, there are fewer studies on the incidence of GC with AM. The mortality of GC with AM increased from 2001 to 2012, but decreased from 2012 to 2016. GC with AM was more frequently discovered in men. And the male incidence showed a steady increase trend, while the female incidence kept a trend of fluctuation.
Our conclusions about the prognosis of MAC were mainly in consistency with previous reports [10–12]. The prognosis of MAC had no difference with CA both in EGC and AGC. In terms of SRCC, SRCC had comparative prognosis with CA in EGC, but poorer prognosis in AGC. Though it’s widely accepted that SRCC is an independent predictor of poor prognosis in advanced gastric adenocarcinomas (GA), the prognosis of SRCC in EGC remains highly controversial [7, 13–16]. In our study, the comparison object of SRCC was CA that was different from previous studies. The reference value of previous researches for our study is questionable.
There were some studies about the clinical characteristics and prognosis of mixed-type EGC based on Lauren's classification [17–19]. According to WHO classification, the mixed carcinoma based on Lauren's classification is different from AM. Adenocarcinoma with mixed subtypes is morphologically a combination of identifiable glandular (tubular/papillary) and signet ring/poorly cohesive cellular components [20].
Our study proved that there were no differences in the aggressive tumor features, such as N stage, M stage, and tumor size between AM and other three histologic subtypes in EGC, which is not consistent with previous researches [9]. We think this is due to the fact that the comparison is not just with adenocarcinoma in the research mentioned above. The number of patients with AM in this research was small. In EGC, AM had a comparative prognosis with CA, MAC and SRCC.
To our knowledge, AM was not well documented in the literature of AGC. In AGC, AM was significantly associated with more aggressive features compared with CA, MAC and SRCC. AGC patients with AM had a poorer prognosis compared with CA and MAC, but a comparative prognosis with SRCC. AM was an independent risk factor for a poor outcome in AGC.
Furthermore, we explored the independent prognostic predictor of GC with AM. In our study, T3-4 stage, N2-3 stage, M1 stage, no surgical modalities of partial gastrectomy and total gastrectomy were proposed to be independent predictors of poor CSS of GC patients with AM. We believe that the establishment of our prognostic scoring system based on GC patients with AM is of clinical significance. We evaluated the value of this nomogram to predict 1- and 3-year CSS rates of GC patients with AM by C-index, calibration curves and ROC curves, which displayed good agreements both in training cohort and validation cohort. Furthermore, DCA demonstrated the benefits and clinical utility of the predictive power of our nomogram.
This study has some limitations. Firstly, this is a retrospective analysis of patients using SEER database. Secondly, we were unable to analyze the disease-free survival of patients and obtain data regarding radiotherapy, chemotherapy and targeted therapies received in localized and advanced disease due to limitations of the database. Thirdly, we didn’t discuss the effect of differentiation on prognosis. Fourthly, selection bias might exist after the case screening. Besides, there were no information of their genotypes, genetic data among these histologic subtypes that may be the prognosis factors, such as human epidermal-growth-factor receptor 2 (HER-2), Microsatellite instable (MSI) and Epstein⁻Barr Virus (EBV) [21–23].