PDCs are rare tumors and are mainly located in the third and fourth portions of the duodenum (45%), followed by the second part of the duodenum (40%) and the duodenal bulb (15%) [6]. Abdominal pain, intestinal obstruction and bleeding are the most common symptoms of adenocarcinoma of the small bowel [7]. However, many patients have nonspecific cancer symptoms [2]. A literature review has reported that the diagnosis of PDCs may be difficult due to the following reasons: symptoms are either mild or nonspecific; tumor markers may be normal or only slightly elevated; and the sensitivity of biopsies is low [5]. Therefore, PDC is often misdiagnosed or missed in the early stage, and it is not diagnosed until symptoms, such as obstruction and jaundice, appear in the late stage [8]. In our case, the patient presented with repeated gastrointestinal bleeding accompanied by occasional epigastric discomfort. Ulceration with hemorrhage was considered previously, but no attention was paid seriously.

The development of advanced endoscopic and imaging methods, as well as an accurate histological examination, allows a better preoperative characterization of duodenal cancer. At present, the main clinical diagnostic methods for duodenal cancer include endoscopy, ultrasonography, magnetic resonance imaging (MRI) and enhanced CT [9]. Endoscopy is the diagnostic modality of choice for the evaluation of PDC, which allows simultaneous visualization and biopsy, with a diagnostic rate of 92.31% [10, 11]. Ultrasonography includes endoscopic ultrasound (EUS) and abdominal ultrasound. EUS can be used to evaluate local extension or lymphadenopathy simultaneously when endoscopy is performed. Abdominal ultrasound can find the dilation of the bile duct and pancreatic duct. However, it is easily affected by abdominal gaseous distension, leading to limitations in clinical application. Enhanced CT and MRI are widely used in assessing tumor depth invasion (T) and regional lymph node invasion (N), which play an important role in assessing the involvement of nearby structures, determining resectability and planning surgery [10, 12]. In cases without a confirmed diagnosis, sensitive but nonspecific radiographic features suggestive of malignancy include an exophytic or intramural mass, central necrosis and ulceration. In addition, for tumors with rich blood supply and hemorrhage, the technique of selective digital subtraction arteriography (DSA) can observe vessel infiltration of the tumor, which is helpful for diagnosis and surgery selection [8].

Surgery is the only radical treatment for SRCC in the duodenum. It has been reported that the 5-year survival rate after radical resection of PDC is approximately 37%-55% [13, 14]. However, there is no clinical data on the 5-year survival rate after radical resection of SRCC, which may be due to the small sample size of cases, indicating that further study is required in the future. Surgical resection is accomplished via four major procedures, including transduodenal excision (transduodenal submucosal excision), local full-thickness resection (wedge resection), pancreas-sparing segmental duodenectomy (PSD), and pancreaticoduodenectomy (PD) [15]. PD has been considered the preferred surgical option for PDC [7, 16, 17]. Cancer can be treated by surgery simultaneously with lymphadenectomy. However, PD is complicated with a high risk of operation and postoperative complications such as biliary fistula and pancreatic fistula. The other three procedures are so-called “limited resections” and are generally utilized for selected tumors not amenable to endoscopic resection that have no or negligible risk of nodal metastasis. Therefore, it may be acceptable that the selection of resection method is determined on the basis of tumor size and histopathological findings of a lymph node using an intraoperative frozen section. For those who are in the late stage of cancer, a palliative operation can be performed to relieve the obstruction of the gastrointestinal or biliary tract, improving the quality of life. Cholangiojejunostomy is often performed together with Roux-en-Y gastrojejunostomy or duodenojejunostomy [18]. Recently, Okamoto T et al. reported that endoscopic resection may be a viable alternative for early SRCC limited to the mucosal layer, thereby providing a new option [5]. In our case, emergency surgery was performed with the main purpose of hemostasis. Only the lesion with hemorrhage was removed during the operation instead of radical resection.

Histologically, there are several theories about the origin of SRCs. One theory suggests that SRCs originate in ectopic gastric mucosa found in the duodenum, while another theory suggests that SRCC arises from gastric type metaplastic epithelium [19,20,21]. In SRCC, the accumulation of mucins such as MUC5AC and MUC2, results in large vacuoles, which may play a role in carcinogenesis [22]. Unfortunately, our hospital could not evaluate mucins, such as MUC5AC or MUC2, due to technical limitations.

The prognosis of SRCC is poor, which may be due, in part, to its more advanced stage. Reports have shown that over 80% of SRCC diagnoses present with advanced disease regardless of the site of origin [19, 20]. In a review of 4995 patients with small bowel adenocarcinoma reported to the National Cancer Database between 1985 and 1995, the overall 5-year survival was 30.5%, and the median survival was 19.7 months; the 5-year survival rates for stage I, II, III and IV were 65%, 48%, 35% and 4%, respectively [23]. Lymph node involvement, curative resection of the tumor and localization of the tumor have an impact on patient survival [24,25,26,27]. In our case, the surgical margin was positive, indicating the poor prognosis of the patient.

Whereas SRCC is thought to be less chemosensitive than non-SRCC, it may have a specific sensitivity profile and be more sensitive to taxane-based chemotherapy or antiangiogenics [28,29,30]. Bang YJ et al. reported that immunotherapy should be tested in SRCC as PDL1 is overexpressed in approximately 23% of cases of SRCC, indicating that an anti-PDL1 monoclonal antibody may be a promising treatment [31]. However, reports have also shown that oncological treatment, such as adjuvant chemoradiotherapy, does not improve survival [13, 25, 32]. Therefore, more prospective trials are needed in the future.

In the present case, the tumor was considered to be primary duodenal bulb cancer due to several reasons. (1) Duodenal ulcer was indicated by endoscopy 2 months ago, and no other lesions were found in the stomach. The patient received a proton pump inhibitor (PPI), but his symptoms did not improve. (2) According to the pathology, the tumor was limited to the mucosal layer and submucosal duodenal gland. The proximal margin was negative, while the distal margin was positive. (3) SRCC was not detected in the stomach histopathologically, and no mass was found elsewhere during the operation. Because of the extensive vascular network that increases the risk of bleeding and the thin, deep muscle layer leading to high perforation rates, duodenal biopsy is not routine, and an experienced endoscopist is critical when performing endoscopic evaluation [33]. For patients whom are diagnosed with ulcers, if symptoms are not improved after regular treatment or the lesion is not healing well when re-examined by endoscopy, pathological biopsy is recommended based on the present case. Multiple samplings should be performed if necessary. Clinically, endoscopy is recommended for patients with dyspepsia aged over 50 or those with alarm features, such as family history of upper-gastrointestinal malignancy, unintended weight loss, gastrointestinal bleeding, iron deficiency anemia, progressive dysphagia, odynophagia, persistent vomiting, palpable mass, lymphadenopathy or jaundice. If there is a clinical suspicion of malignancy, even in the absence of alarm features, endoscopy should also be considered [34].

In conclusion, we report a rare case of SRCC in the duodenal bulb. The diagnosis of PDCs is difficult due to mild and nonspecific presenting symptoms, normal or only minimally elevated tumor markers, and low sensitivity of biopsies. For patients who can receive radical tumor resection, PD should be considered as the first choice. The prognosis of PDC is potentially improved through early diagnosis and radical surgical resection.

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