A Rare Case of Aggressive Systemic Mastocytosis Involving the Gastrointestinal System and Review of Literature

Systemic mastocytosis is a rare disease and most patients have pigmented urticarial skin lesions. It can be easily missed and misdiagnosed in small biopsies, especially in those patients with nonspecic clinical complaints or untypical skin lesions. We report a case of 69-year-old man who have presented with 2-year of diarrhea, progressive weight loss of 20kg and abdominal distention for 3 months. Ultrasound and abdominal CT scan showed massive effusions in abdominal and pelvic cavity. Colonoscopy was performed and showed intensive mucosal proliferations forming polypoid appearances. Microscopically, monotonously uniform, small, round tumor cells with slightly rich cytoplasm were concentrated between the residual glands in the colonoscopic biopsy. The tumor cells showed positive expression of CD117 and S-100, and low Ki-67 proliferation index of 2%, while Trypsin, CK, CD68, CD1a, Langerin, Syn, CgA, CD56, SATB2, CD20, CD3, α-inhibin and SMA were all negative. KIT D816V mutation was detected as well. Liver biopsy showed that CD117 positive cells were more than 15 cells in aggregates around the hepatic portal area and less than 15% mast cells were found in bone marrow smears. No multiple or diffuse pattern of mast cells inltration was seen by repeated skin biopsies of skin lesions. With all these considered, the diagnosis of aggressive systemic mastocytosis was made. CgA: Chromogranin A; CD1a: Cluster of differentiation 1a; CD56: Cluster of differentiation 56;SATB2: special AT-rich sequence binding protein 2; CD20: Cluster of differentiation 20; CD3: Cluster of differentiation 3; SMA: Smooth muscle actin


Abstract
Background Systemic mastocytosis is a rare disease and most patients have pigmented urticarial skin lesions. It can be easily missed and misdiagnosed in small biopsies, especially in those patients with nonspeci c clinical complaints or untypical skin lesions.

Case presentation
We report a case of 69-year-old man who have presented with 2-year of diarrhea, progressive weight loss of 20kg and abdominal distention for 3 months. Ultrasound and abdominal CT scan showed massive effusions in abdominal and pelvic cavity. Colonoscopy was performed and showed intensive mucosal proliferations forming polypoid appearances. Microscopically, monotonously uniform, small, round tumor cells with slightly rich cytoplasm were concentrated between the residual glands in the colonoscopic biopsy. The tumor cells showed positive expression of CD117 and S-100, and low Ki-67 proliferation index of 2%, while Trypsin, CK, CD68, CD1a, Langerin, Syn, CgA, CD56, SATB2, CD20, CD3, α-inhibin and SMA were all negative. KIT D816V mutation was detected as well. Liver biopsy showed that CD117 positive cells were more than 15 cells in aggregates around the hepatic portal area and less than 15% mast cells were found in bone marrow smears. No multiple or diffuse pattern of mast cells in ltration was seen by repeated skin biopsies of skin lesions. With all these considered, the diagnosis of aggressive systemic mastocytosis was made.

Conclusions
The diagnosis of aggressive systemic mastocytosis is challenging for untypical clinical manifestations and subtle or inconspicuous lesions, especially in endoscopic biopsies, which requires awareness and a close teamwork of pathologists and clinicians. Background Mastocytosis (MC) is a heterogeneous group of disorders characterized by abnormal growth, neoplastic proliferation and accumulation of mast cells. Approximately 80% of patients with MC have the evidence of skin involvement, while the rest may involve the gastrointestinal tract, liver, spleen or bone [1]. Three variants of MC are recognized mainly by clinicopathological ndings and classi ed as Cutaneous MC, Systemic mastocytosis (SM) and mast cell leukemia. The diagnosis of MC is made when it meets the World Health Organization diagnostic criteria of neoplastic mast cells in ltration. The diagnosis of SM can be made if the major criterion and at least 1 minor criterion are present, or above 3 minor criteria are satis ed [2]. Aggressive systemic mastocytosis (ASM) is an unusual subtype of SM (12%) and can be diagnosed when the SM patients have more than one "C" nding but do not meet the criteria for mast cell leukemia. When the gastrointestinal system is involved by SM, nonspeci c symptoms such as abdominal pain, diarrhea, and vomiting are complained. Overlapping clinical manifestations make the histological diagnosis extremely di cult. Especially those cases with isolated symptoms and no prior diagnosis can be easily ignored. Here, we report a case of ASM with gastrointestinal manifestations of unusual clinic and pathologic manifestations which is rarely reported.

Case Presentation
The patient was a 69-year-old man with 2-year history of diarrhea, progressive weight loss of 20kg and abdominal distention for 3 months. He complained for 1 to 2 yellow and mushy stools daily at rst, and then gradually increased to 4 or 5 times daily. After intermittent anti-Helicobacter pylori treatment, the clinic symptoms were not improved effectively. The symptom of diarrhea still occurred 4 to 5 times a day after stopping drugs. After six months treatment, side effects of nausea and persistent diarrhea with fatigue appeared so the treatments were suspended. Three months later, the patient developed pitting edema and abdominal distension. He was admitted to another local hospital for further treatments.
Colonoscopy showed diffuse polypoid hyperplasia in transverse colon, ascending colon and ileocecal region with a pathological diagnosis of tubular adenoma. Ultrasound and abdominal computed tomography (CT) scan showed massive effusions in abdominal and pelvic cavity and multiple cysts in liver and kidney. The bone density was unevenly distributed by three-dimensional rebuilding of abdominal CT (Fig. 1).
Before the last admission in June 1st, 2020, gastroscopy and colonoscopy were performed again.
Colonoscopy showed intensive mucosal proliferations forming polypoid appearances with a diameter of 0.2cm to 1.2cm from ileocecum to the junction of descending and sigmoid colon (Fig. 2), while gastroscopy showed no obvious abnormalities except for focal mucosa atrophy. Colonoscopic biopsy showed that the mucosal glands of ileocecal valve and hepatic exure were atrophic, with blunt villous, reduced crypt and uneven distributed glands. Monotonously uniform, small, round tumor cells with slightly rich cytoplasm were concentrated between the residual glands (more than 15 tumor cells in aggregates). The tumor cells had round, oval and spindle nuclei with ne chromatin and no mitoses were detected. Among the tumor cells, a large amount of eosinophils in ltrations were observed (Figs. 3 and 4). The tumor cells showed positive expressions of CD117 and S-100, and low Ki-67 proliferation index of 2%. Trypsin, CK, CD68, CD1a, Langerin, Syn, CgA, CD56, SATB2, CD20, CD3, α-inhibin and SMA were all negative (Fig. 5). Basophilic granules were found in the cytoplasm by Giemsa staining. C-KIT gene detection was further performed to con rm the diagnosis. The results revealed C-KIT gene c.2447A > T (p.d816v) mutation in exon 17 (Fig. 6). Gastroscopic biopsy also showed that there were a few scattered small and round cells of more than 15 tumor cells in aggregates with eosinophils in ltrations between the normal glands. These small clusters of cells were positive for CD117. Thus the diagnosis of SM was con rmed.
As most SM patients were reported to have skin lesions, a close physical examination was done in this case. Brownish red rash and pigmentation was found all over his body with a diameter of 0.5cm to 0.8cm. Most of them were on the trunk or bilateral upper limbs with symmetrical involvement. The skin scratch test was weakly positive and no urticaria was found on both sides of the lower limbs. The patient complained that he would develop red macules and pruritus on the skin when faced with cold wind or other irritations for 40 years. However, he was treated as eczema in the past years (Fig. 7). To determine whether there was a skin involvement, skin biopsies were repeated twice, while, microscopically, only scattered mast cells in the subcutaneous tissues were outlined by CD117 immunohistochemistry staining.
To explore the ndings in the CT scan and evaluate the extent of SM involvement, liver biopsy and bone marrow aspirate was performed. Liver biopsy showed that clusters of CD117 positive cells of more than 15 tumor cells in aggregates were located around the hepatic portal area with focal lobular necrosis or fusion necrosis around the central vein (Fig. 8). Bone marrow smears revealed less than 15% mast cells.
The nal diagnosis of ASM was con rmed and the patient had the six times neoadjuvant chemotherapy with Cladribine treatment till March 29, 2021. Bone marrow smear was repeated twice and ow cytometric determination was done, while none of those tests results met the criteria for mast cell leukemia. This patient was in remission as less than 1% mast cells were found in the latest bone marrow smear.

Discussion
MC was a rare group of disorders of unknown etiology and de ned as abnormal proliferation of mast cells. Abnormal mast cells and their mediators could affect many organs and the manifestations might vary differently. Nearly 60-80% of the SM patients had the gastrointestinal system manifestations such as abdominal pain (51%), diarrhea (43%), vomiting (28%), nausea and malabsorption. These symptoms could be a response to the mast cells mediators or direct in ltration [1,3,4]. However, gastrointestinal manifestations were not speci c and could be easily misdiagnosed. Serum total tryptase levels, as a minor criterion, were helpful if it reached over 20ng/ml. But in this case, the serum tryptase level was not tested before the diagnosis. This patient was misdiagnosed with non-speci c gastrointestinal symptoms in the local hospital.
Nearly half of the SM had skin lesions and skin symptoms were more common in indolent SM than ASM [1]. Although 61% of those SM had gastrointestinal manifestations, few had mast cells aggregates under endoscopic biopsies [5]. This patient was diagnosed by close pathological examinations before skin symptoms were noticed. Although this patient had brownish red rash and pigmentation all over the body and he would develop red macules and pruritus when faced with cold wind or other irritations in the past 40 years, the skin scratch test was just weakly positive. Microscopically, only scattered mast cells were seen by repeated skin biopsies instead of clusters or diffuse patterns of mast cells in ltrations. Further studies were still needed to investigate the possible disease progression from cutaneous MC to ASM.
Endoscopy with biopsies was the most common procedures performed on patients of SM with nonspeci c gastrointestinal complaints. In 60% of the cases, the most frequently observed lesions were small nodules, mucosal edema and polypoid lesions in the intestinal tract, while the other might appear endoscopically unremarkable [6,7]. In some cases, ulcerations had been reported and could result to a wrong impression of in ammatory bowel diseases [8]. No special disorders were observed in esophagus and stomach except gastric ulcers, esophageal re ux, in ammations and nodular mucosa. Therefore, multiple serial biopsies was needed when the patient had continuous gastrointestinal complaints [9]. The main endoscopic features were polypoid appearances formed by intensive mucosal proliferations, which had no visible abnormalities. Thus biopsies remained a critical step to further diagnosis [10].
Pathologically, mast cells were usually scattered in healthy individuals, without any clinical implications.
Only a few subtle and multifocal clusters of mast cells in ltrations could be seen in nearly 23.5-74.3% of MC patients, and could be easily missed and mistaken for histocytes in random endoscopic biopsies, not to mention those dispersed mast cells in the background of in ammation [9]. It was notable only in a diffuse in ltration pattern or multifocal clusters. The major criterion of SM was clusters of more than 15 mast cells in any extracutaneous tissues. Mast cells were most commonly seen under the crypts or at the top of the villi [7]. Mast cells were uniform, small, round cells with slightly rich cytoplasm accompanied by prominent eosinophilic in ltrations. Sometimes, mast cells could be atypical with spindle morphology or reduced granularity. Few mitoses could be seen.
CD117 was expressed in both normal and neoplastic mast cells. CD25, CD2 or both were reliable markers to distinguish neoplastic from normal mast cells [11,12]. CD25 staining was particularly effective in the bone marrow rather than in extramedullary tissues, because there was a few CD25 positive lymphatic cells in the background [13]. High expression of CD25 had a close relationship with C-KIT gene D816V mutation, which was related with poor prognosis in SM patients, while wild type C-KIT status was correlated to the absence of CD25 in most cases [7]. Unfortunately, we did not have CD25 antibody and CD2 was not positive in the endoscopy or liver biopsies. KIT D816V mutation, as a minor criterion of SM, was found up to nearly 85% in the bone marrow, blood or another extracutaneous organ of all patients with SM [14]. However, diagnosis of SM could not be completely excluded by false-negative results of KIT D816V mutation due to insu cient samples when tested in endoscopic biopsies. KIT D816V mutation was not only presented in MC but also could be seen in other lymphomas or soft tissue tumors. Besides, other oncogenes in variants of KIT mutation, somatic mutations of TET2, SRSF2, ASXL1, RUNX1, JAK2, NRAS and KRAS and pro-oncogenic key mutants of CALR, PDGFRA, PDGFRB mutations were also identi ed [15].
Liver involvement was common in ASM and might lead to abnormal liver laboratory examinations, ascites and/or portal hypertension. This patient had the characteristic features of SM and progressive weight loss of 20kg with ascites and liver biopsy con rmed the diagnosis of ASM. Bone marrow smears of less than 20% mast cells did not meet the diagnosis of the mast cell leukemia. ASM diagnosis was made due to the major criterion and one minor criterion of SM and had at less two "C" ndings of ascites with impairment of liver function and malabsorption with signi cant weight loss, while the bone marrow smears of less than 20% mast cells did not reach the mast cell leukaemia diagnosis. ASM was further divided into untransformed form and transformed form. ASM in transformed form had 5% 19% MCs in bone marrow smears and could frequently progress to MCL of poor prognosis [16].
ASM was a rare disease which needed to be ruled out from other tumors when it showed a diffuse pattern between the residual glands with rare tumor formations. The differential diagnoses included reactive hyperplasia of histiocytes, neuroendocrine tumors, langerhans cell histiocytosis, poorly differentiated adenocarcinoma, soft tissue tumors and lymphomas. They had partially similar histopathological characteristics but could be easily distinguished by a group of immunohistochemical markers. Another important feature was that a large amount of eosinophilic granulocytes among the mast cells could be seen, whereas only a few eosinophilic granulocytes could be present in nonspeci c in ammations or in ammatory bowel diseases in the intestine. To date, there was no generally accepted rst-line treatment for patients with ASM of abdominal symptoms of pain and/or diarrhea, treatment was intended to avoid mast cell deregulations and inhibit the actions of the constitutive mediators released by mast cells including H1/H2 antihistamines, proton pump inhibitors and antileukotrienes. For severe cases, cytoreductive agents of interferon alpha, Glucocortioids (especially with severe malabsorption or ascites) and Cladribine, Tyrosine kinase inhibitors and hematopoietic stem cell transplant were optional [17]. Abdominal CT scan revealed that multiple cysts in liver and kidney and massive effusions in abdominal and pelvic cavity. The bone density was unevenly distributed in the scanning eld by three-dimensional rebuilding.

Figure 2
Colonoscopy showed intensive mucosal proliferations forming polypoid appearances with a diameter of 0.2cm to 1.2cm from ileocecum to the junction of descending and sigmoid colon Figure 3 Between the residual glands, monotonously uniform, small, round tumor cells with slightly rich cytoplasm were seen.  The tumor cells had round, oval and spindle nuclei with ne chromatin and no mitoses were detected.  c.2447a > t (p.d816v) mutation was found in KIT exon 17.

Figure 7
The patient had brownish red rash and pigmentation all over the body with a diameter of 0.5cm 0.8cm, mostly on the trunk or bilateral upper limbs with symmetrical involvement.