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Primary Pancreatic Diffuse Large B-Cell Lymphoma Involving the Stomach

Correspondence to Tae Joo Jeon, M.D., Ph.D. Division of Gastroenterology, Department of Internal Medicine, Sanggye Paik Hospital, Inje University College of Medicine, 1342 Dongil-ro, Nowon-gu, Seoul 01757, Korea Tel: +82-2-950-1341, Fax: +82-2-950-1955, E-mail: drjtj@paik.ac.kr Copyrightc 2020 The Korean Association of Internal Medicine This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 위를 침범한 원발성 췌장 미만성 거대 B세포 림프종


INTRODUCTION
Primary pancreatic lymphoma (PPL) is a rare form of extranodal malignant lymphoma, comprising 1% of all extranodal lymphomas and 0.5% of all pancreatic masses [1,2]. Because PPL and pancreatic adenocarcinoma have similar clinical presentations and imaging findings, histological examinations are needed to differentiate these cancers [2][3][4]. Differentiation of PPL and adenocarcinoma is important because of the different treatment options that improve prognosis for affected patients [3]. We report a rare presentation of lymphoma as a primary pancreatic tumor involving the stomach.
Abdominal computed tomography (CT) showed a well-defined hypodense mass located at the pancreas head and involving the stomach, as well as enlargement of several mesenteric and perigastric lymph nodes (Fig. 1). Upper gastrointestinal endoscopy revealed multiple geographic ulcers on the gastric body and antrum; therefore, histological examination was performed (Fig. 2).

DISCUSSION
The pancreas is a rare extranodal site of non-Hodgkin lymphoma; the most common histological subtype of PPL is diffuse large B-cell lymphoma, which is present in 80% of patients with PPL [3,5]. PPL is generally diagnosed when the bulk of the disease is localized to the pancreas, with adjacent lymph node involvement and potentially distant spread [6]. Dawson  However, no patient has been described with PPL involving the stomach. When lymphoma involves multiple organs, the primary site cannot be differentiated by pathologic findings or immunohistochemical staining [2]. We defined the primary lesion as the largest mass. In our patient, the large mass was predominantly located in the pancreas and was distinct from the gastric wall. Furthermore, pancreatic duct dilatation and mediastinal lymphadenopathy were not observed.
There is no specific clinical manifestation suggestive of PPL [1]. The most common symptoms are epigastric pain, a palpable abdominal mass, and weight loss [1][2][3]5]. Jaundice is infrequent in patients with PPL, despite a large mass at the head of the pancreas [6]. Symptoms often observed in patients with other lymphomas (e.g., fever, night sweats, and weight loss) are rarely present in patients with PPL [5]. Our patient complained of epigastric pain and weight loss, commonly associated with lymphomas.
Because laboratory test results are nonspecific, they do not aid the diagnosis of PPL [1]. The serum CA19-9 level is normal or slightly elevated in patients with PPL, unless biliary obstruction is present, whereas 80% of patients with pancreatic adenocarcinoma have a high CA19-9 level [1]. The serum lactate dehydrogenase and β2-microglobulin levels are often high in patients with lymphoproliferative diseases (e.g., lymphoma), but they are inevitably not increased in patients with PPL; moreover, elevated lactate dehydrogenase and β2-microglobulin levels are not required for the diagnosis of PPL [1,5]. However, higher lactate dehydrogenase and β2-microglobulin levels are indicators of A B -박지영 외 1인. 췌장의 미만성 거대 B세포 림프종 --285 -a poor prognosis for patients with PPL [5]. Our patient had no specific findings in laboratory tests; his CA19-9 and lactate dehydrogenase levels were within normal ranges.
Contrast-enhanced CT is the imaging modality of choice for evaluation of a pancreatic mass [11]. PPL can be divided into two typical morphological groups on CT: 1) a localized, well-circumscribed tumoral form, and 2) a diffuse enlargement infiltrating or replacing most of the pancreatic gland. As in our patient, a bulky localized tumor in the pancreatic head without significant main pancreatic duct dilatation and with significant lymphadenopathy below the level of the renal veins, suggestive of PPL, is observed by CT [11]. Endoscopic ultrasound has also been widely used to evaluate pancreatic masses and surrounding structures; it is more sensitive than CT for detection of small lesions [1]. Furthermore, tissue sampling can be performed by endoscopic ultrasound-guided fine-needle aspiration or by biopsy with high sensitivity and specificity [4]. Positron emission tomography is helpful in the staging of lymphoma, differentiation of malignant from benign lesions, and evaluation of therapeutic response [11]. Although radiological examinations can provide support in the diagnosis of PPL, they are unable to distinguish between PPL and other pancreatic lesions. Therefore, clinicians must obtain cytohistological evidence for a definitive diagnosis of PPL [1].
The treatment strategy for PPL consists of surgery, radiotherapy, chemotherapy, or a combination thereof [12]. The role of surgery is controversial; aggressive surgical approaches that include pancreatic resection or tumor debulking are not preferential to chemotherapy because of the risk of surgical complications [3]. Surgical resection may play a role in the treatment of localized pancreatic lymphoma [12]. The role of radiotherapy also remains undefined; it is considered an adjuvant to chemotherapy [3]. The majority of patients with PPL receive chemotherapy alone [1,12]. The first-line chemotherapy regimen is prednisolone-vincristine-doxorubicin-cyclophosphamide (CHOP) [12]. CHOP chemotherapy in combination with rituximab (R-CHOP) was recently used for treatment of a patient with DLBCL that exhibited CD20 positivity [1]. Our patient's tumor was positive for CD20 by immunohistochemical staining; thus, he underwent R-CHOP chemotherapy.
In conclusion, we present a rare instance of PPL involving the stomach, with symptoms including epigastric pain and weight loss. Diagnosis was made by endoscopic ultrasound-fine-needle aspiration and biopsy. PPL is a rare neoplasm, but should be considered in the differential diagnosis of pancreatic tumors.
Because PPL is potentially curable and has a much better prognosis than adenocarcinoma, a correct diagnosis based on histological examination is important. The treatment strategy for PPL is controversial, but combination chemotherapy may be optimal.