Background Persistent descending mesocolon (PDM) is a congenital anomaly associated with the failure of fixation of the descending colon to the lateral abdominal wall. In the laparoscopic colectomy for colorectal cancer, it has been noticed that there are extensive adhesions and a distinctive anatomy of colonic vessels in cases with PDM. Therefore, it is necessary to have sufficient knowledge about PDM so that it can be appropriately treated during surgery. Case presentation Case 1—a 79-year-old man underwent laparoscopic intersphincteric resection for rectal cancer. Preoperative barium enema (BE) revealed that the sigmoid colon was located at the right side of the abdomen. An enhanced computed tomography (CT) showed that the common trunk of the left colic artery (LCA) and the first sigmoid colonic artery (S1) branched from the inferior mesenteric artery (IMA). Case 2—a 68-year-old man underwent laparoscopic sigmoidectomy for sigmoid colon cancer and laparoscopic distal gastrectomy for gastric cancer synchronously. BE showed that the descending colon ran from the splenic flexure to medial caudal side. An enhanced CT showed that the distance from the LCA to the marginal artery was 1.0 cm. Case 3—a 68-year-old man underwent laparoscopic low anterior resection for rectal cancer. BE showed that the descending colon ran to the medial caudal side. An enhanced CT showed that the mesentery of the descending colon was comparatively shortened. Case 4—a 60-year-old man underwent laparoscopic sigmoidectomy for sigmoid colon cancer. An enhanced CT showed that the descending colon ran to the medial caudal side and predicted that the LCA and S1 formed a common trunk and branched radially from the IMA. We reported four cases with PDM recognized preoperatively as above. Three cases had a shortening of the mesocolon. While dissecting the vessels, although special attention was required to maintain the blood flow to the intestine, none of these cases developed any complications during the postoperative course. Conclusions We considered that it is important to have positional awareness of the LCA and the marginal artery to perform the laparoscopic surgery safely when a colorectal cancer with PDM is diagnosed preoperatively using imaging methods.

Background Schloffer tumor is a foreign body granuloma in the abdominal subcutaneous layer that develops due to a foreign body such as suture from several months to years postoperatively. Herein, we report a case of a rapidly growing Schloffer tumor with F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) positivity at the port site of laparoscopic sigmoidectomy for colon cancer. Case presentation An 85-year-old man, who underwent laparoscopic sigmoidectomy for stage IIIa sigmoid colon cancer 10 months ago, was referred to our hospital with complaints of a growing mass in the abdominal wall. The tumor was palpable at the right-sided abdominal wall corresponding to the port site of laparoscopic sigmoidectomy. The tumor rapidly grew for 2 months. Computed tomography showed a ring-enhanced mass at the right-sided abdominal wall. PET examination revealed high accumulation of FDG in the tumor. Tumor resection was performed due to suspected port site recurrence. The pathological diagnosis was inflammatory granuloma, so-called Schloffer tumor. Conclusion In the era of laparoscopic surgery, Schloffer tumor may be one of the differential diagnoses for rapidly growing tumor with FDG-PET positivity at the port site in postoperative patients with advanced colorectal cancer.

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Synthetic lethality is a promising therapeutic strategy, but the number of founder mutations is limited. In contrast, DNA methylation is frequently present in many types of cancers, and can be a potential target for a synthetic lethality. So far, BRCA1 methylation with a PARP inhibitor is known as a synthetic lethality [Kawachi et al., Breast Cancer Res Treat, 181:323-329, 2020]. In this study, we aimed to identify a novel methylation synthetic lethal combination in gastric cancers. Founder methylation was searched for in 8,008 genes with putative promoter CpG islands (CGIs), and 137 genes which were 1) heavily methylated and 2) frequently methylated in primary gastric cancers (10 or more of 50 cases) were selected. The association analysis between DNA methylation and gene expression showed that 10 of 137 genes were completely silenced in gastric cancer cell lines with methylation of their promoter CGIs, but were expressed in those without. Among these 10 genes, we focused on CHFR, a known tumor-suppressor gene in gastrointestinal cancers, and genes lethal for CHFR methylation were screened for using the sgRNA screening database (The Cancer Dependency Map, DepMap). Comparison of gene dependencies of 17,645 genes between four cell lines with CHFR methylation and 12 cell lines without revealed that knockout of KRAS reduced cell growth specifically in cell lines with methylation. This synthetic lethality could be experimentally confirmed in two cell lines with CHFR methylation, AGS and 44As3, and three cell lines without, HSC41, HSC42, and MKN74. These cell lines included those not used in the screening, validating the usefulness of the combination. These results showed that gastric cancers with CHFR methylation were sensitive to KRAS inhibition, and that methylation synthetic lethality is a promising therapeutic strategy. Citation Format: Hideyuki Takeshima, Takahiro Ebata, Yumi Furuichi, Satoshi Yamashita, Toshikazu Ushijima. Methylation synthetic lethality: CHFR methylation and KRAS inhibition in gastric cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6015.

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