Clinical Features of Gastric Signet Ring Cell Cancer : Results from a Systematic Review and Meta-Analysis

The clinical behaviour of signet ring cell histology in gastric cancer has long been a subject of controversy. Recent years have underscored the pressing issue of a lack of a standardised definition for signet ring cell histology, leading to its often-ambiguous placement within broader categories associated with poor prognosis. Conversely, comparisons of signet ring cell gastric cancer have been made against a wide spectrum of non-signet ring cell cases, introducing significant heterogeneity. The primary objective of this literature search and subsequent meta-analysis was to gain a deeper understanding of signet ring cell gastric cancer. Our findings revealed that the prognosis of signet ring cell gastric cancer is intricately tied to the disease stage, yet it is also contingent on the specific comparison group employed. The variability in signet ring cell cancer's clinical behaviour may stem from the absence of a standardised definition. Therefore, it is imperative to work towards a uniform classification system for gastric cancer to enhance clarity and coherence in future research and clinical practice. Conflicting results about the prognostic relevance of signet ring cell histology in gastric cancer have been reported. We aimed to perform a meta-analysis focusing on the clinicopathological features and prognosis of this subgroup of cancer compared with other histologies. A systematic literature search in the PubMed database was conducted, including all publications up to 1 October 2021. A meta-analysis comparing the results of the studies was performed. Results: A total of 2062 studies referring to gastric cancer with signet ring cell histology were identified, of which 262 studies reported on its relationship with clinical information. Of these, 74 were suitable to be included in the meta-analysis. A slightly lower risk of developing nodal metastases in signet ring cell tumours compared to other histotypes was found (especially to undifferentiated/poorly differentiated/mucinous and mixed histotypes); the lower risk was more evident in early and slightly increased in advanced gastric cancer. Survival tended to be better in early stage signet ring cell cancer compared to other histotypes; no differences were shown in advanced stages, and survival was poorer in metastatic patients. In the subgroup analysis, survival in signet ring cell cancer was slightly worse compared to non-signet ring cell cancer and differentiated/well-to-moderately differentiated adenocarcinoma. Most of the conflicting results in signet ring cell gastric cancer literature could be derived from the lack of standardisation in their classification and the comparison with the different subtypes of gastric cancer. There is a critical need to strive for a standardised classification system for gastric cancer, fostering clarity and coherence in the forthcoming research and clinical applications.