Histopathological response to chemotherapy and survival of mucinous type gastric cancer.

Background: Data on the clinicopathological characteristics of mucinous gastric cancer (muc-GC) are limited. This study compares the clinical outcome and response to chemotherapy between patients with resectable muc-GC, intestinal (int-GC) and diffuse (dif-GC) gastric cancer.

Methods: Patients from the D1/D2 study or the CRITICS trial were included in exploratory surgery-alone (SAtest) or chemotherapy test (CTtest) cohorts. Real-world data from the Netherlands Cancer Registry on patients treated between with surgery-alone (SAvalidation), and receiving preoperative chemotherapy with or without postoperative treatment (CTvalidation) were used for validation. Histopathological subtypes were extracted from pathology reports filed in the Dutch Pathology Registry and correlated with tumor regression grade (TRG) and relative survival (RS).

Results: In SAtest (n = 549) and SAvalidation (n = 8062) cohorts, muc-GC patients had a five-year RS of 39% and 31%, similar to or slightly better than dif-GC (43% and 29%, p = .52 and p = .011), but worse than int-GC (55% and 42%, p = .11 and p < .001). In CTtest (n = 651) and CTvalidation (n = 2889) cohorts, muc-GC showed favorable TRG (38% and 44% (near-)complete response) compared to int-GC (26% and 35%) and dif-GC (10% and 28%, p < .001 and p = .005). The 5-year RS in CTtest and CTvalidation cohorts for muc-GC (53% and 48%) and int-GC (58% and 59%) was significantly better compared to dif-GC (35% and 38%, p = .004 and p < .001).

Conclusion: Recognizing and incorporating muc-GC into treatment decision-making of resectable GC can lead to more personalized and effective approaches, given its favorable response to preoperative chemotherapy in relation to int-GC and dif-GC and its favorable prognostic outcomes in relation to dif-GC.