You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
the gastrointestinal tract ( gi ) is a common site of presentation for extranodal lymphomas , which comprise between 5 and 10% of all primary gi neoplasms .
the commonest type of primary gi lymphoma is diffuse large b - cell lymphoma , which is a type of non - hodgkin 's lymphoma and accounts for about 45% of all cases of primary gi lymphoma .
mucosa - associated lymphoid tissue lymphoma ( malt lymphoma or maltoma ) , also known as extranodal marginal zone b - cell lymphoma , is a subtype of b - cell non - hodgkin 's lymphoma and comprises approximately 17% of all gi tract lymphomas .
peyer 's patches , found in the small intestine , are examples of prominent , normal malt .
antigenic stimulus in the gi tract , e.g. helicobacter pylori ( hp ) infection in the stomach , leads to the activation of the gi immune response and the proliferation of malt . in the presence of sustained antigenic stimulus , lymphocytes within the malt
maltomas are not limited to the gi tract and can occur at any site in which malt is able to proliferate .
they can arise not only in response to the chronic inflammation seen in infections such as hp gastritis , but also in response to the chronic inflammation seen in autoimmune conditions such as sjogren 's syndrome , where they can occur in the salivary glands and in the thyroid in response to hashimoto 's thyroiditis .
the commonest gi site of maltoma is the stomach , with approximately 50% of lesions arising here , most commonly in response to chronic hp infection .
less common sites include the small bowel , which accounts for 2030% , and the colon , with colonic maltomas being relatively rare and only accounting for approximately 10% of all gi maltomas .
although maltomas themselves are not uncommon , the presence of synchronous upper and lower gi maltomas appears to be a more rare occurrence , with only a few cases reported [ 2 , 3 , 4 ] .
here we present a case of synchronous upper and lower gi maltomas and the potential management difficulties of maltomas .
a 73-year - old man with type 2 diabetes mellitus was referred from primary care with a 4-month history of alternating bowel habit associated with excessive mucus .
there was no rectal bleeding and he did not have any abdominal pain , nor had he lost any weight .
his abdomen was soft and non - tender and there were no palpable masses or organomegaly .
g / l , a white blood cell count of 3.1  10/l , a neutrophil count of 1.7  10/l , platelets 203  10/l , sodium 140 mmol / l , potassium 5.1 mmol / l , urea 7.8 mmol / l , creatinine 94 mol / l , albumin 43 g / l , bilirubin 4 mol / l , alanine aminotransferase 15 iu / l and alkaline phosphatase 36 iu / l .
he underwent a colonoscopy , which revealed a large 5-cm , ulcerated , polypoid sigmoid lesion ( fig .  1 ) .
potential diagnoses at this point included colonic cancer , gastrointestinal stromal tumour ( gist ) or maltoma . the biopsies from this lesion showed an intense lymphoid infiltrate , but no overt evidence of adenocarcinoma .
subsequent immunohistochemical ( ihc ) analysis showed a lymphoid infiltrate with numerous cd20 + b cells .
bcl-2 was positive , whilst cyclin d1 , cd10 , cd43 and bcl6 were negative .
the patient underwent a staging ct scan , which confirmed the sigmoid lesion but also revealed a gastric cardia mass , but showed no evidence of other metastases .
an oesophagogastroduodenoscopy revealed nodular gastritis throughout the corpus and a 30-mm spherical mass in the cardia with some proximal ulceration ( fig .  2 ) .
he also underwent a linear endoscopic ultrasound which confirmed a 30-mm smooth heterogenous hypoechoic lesion that involved mucosa , submucosa and the muscularis propria ( fig . 
fine needle aspiration samples from the cardia mass revealed that there were no spindle cells present , which excluded a gist .
the biopsies from the gastric lesion , similarly to the sigmoid lesion , showed a dense lymphoid infiltrate and similar immunohistochemistry ( fig . 
4 ) , with the exception that the gastric biopsies were cd43 positive on immunohistochemistry , whilst the colonic lesion was negative .
this resulted in a diagnosis of synchronous upper and lower gi tract maltomas , with differing immunohistochemistry patterns  multi - focal malt lymphoma .
fluorescence in - situ hybridisation ( fish ) studies of both sets of biopsies were conducted to assess for the presence of the malt1 translocation  these were negative .
the patient underwent a sigmoid resection for the lesion which confirmed that the sigmoid lesion was a maltoma .
the gastric maltoma did not respond to either successful hp cure or a course of rituximab ; however , after 3 cycles of bendamustine and rituximab chemotherapy , a repeat ct scan showed near complete resolution of the gastric lesion .
the diagnosis of maltoma usually relies on the careful application of histological and ihc analyses of the biopsy samples obtained during endoscopy .
histology will show the presence of lymphoepithelial lesions , defined by the infiltration and distortion of epithelial structures by aggregates of ( usually three or more ) neoplastic lymphoid cells . despite there being no specific ihc marker for maltoma ,
the ihc pattern is virtually identical to that of nonneoplastic marginalzone b cells : cd20 + , igd , igm ( > iga > igg)+ , cd5 , cd10 , cyclin d1 .
attempts have been made to determine the key endoscopic features which would suggest a lesion is a maltoma .
gastric maltomas have had a 6-point classification proposed : ( 1 ) exophytic : a single mass with irregular or polypoid aspect ; ( 2 ) ulcerative : single to multiple ulcerations / erosions ; ( 3 ) hypertrophic : enlarged folds and nodular pattern ; ( 4 ) petechial haemorrhage : several petechiae at mucosal level ; ( 5 ) normal / hyperemic mucosa : normal to reddish mucosa , and ( 6 ) mixed : more of the above - mentioned pattern present .
the role of endoscopic ultrasound was also covered and the authors concluded that 4 tumour patterns can be present : ( 1 ) superficial : where there is thickening of the second and third layers without involvement of either the first or fourth layer ; ( 2 ) diffuse - infiltrative : diffuse trans - mural involvement of the gastric wall with irregular layer border and absence of uniform echogenicity ; ( 3 ) mass - forming : localized hypoechoic mass at the third / fourth layer , with good demarcation from the surrounding tissue , and ( 4 ) mixed - type : a combination of the previous three patterns .
colonic maltomas are much rarer and make a consensus harder to arrive at , but the review suggested the usual endoscopic appearance is of a whitish polypoid lesion , usually not ulcerated and 12 cm in diameter , preserving a smooth aspect at endoscopy .
gastric maltoma is regarded as an indolent disease , and the conventional treatment for low - grade gastric maltoma is hp cure .
approximately 20% of patients do not respond to hp cure and will require treatment with rituximab with or without chemotherapy .
interestingly , the absence of malt1 translocation is usually an indicator of probable successful response to hp cure , although this was not the case in our patient .
the treatment for colonic maltoma depends on the patients age , co - morbidities , disease stage , etc . , but usually involves a combination of surgery and/or rituximab + / chemotherapy [ conventionally chop ( cyclophosphamide , doxorubicin , vincristine and prednisolone , although bendamustine with rituximab is also used ] .
in this case , a 72-year - old man presented with a few months of altered bowel habit . he was found to have a sigmoid lesion , which later proved to be maltoma .
a staging ct scan showed a synchronous gastric lesion , which was also found to be a maltoma after biopsy .
interestingly , the two lesions were shown to have a slightly different ihc profile , thus leading to a diagnosis of multifocal malt lymphoma .
although rare in the literature , the presence of cases such as this does raise the question of whether all patients with confirmed maltoma in the gi tract , especially gastric maltoma , should undergo staging ct and colonoscopy to exclude synchronous lesions .
complete staging has been suggested as mandatory by fischbach   in his review on current maltoma diagnosis and management , and the classification should be based on either the ann - arbor system or the tmn system , although the latter has not been validated .
currently , patients with confirmed gastric maltoma are unlikely to have a ct scan due to the belief that it is an indolent disease .
the detection of synchronous lesions will obviously affect their long - term prognosis and care , as synchronous lesions will likely require far more aggressive therapy than low - grade isolated gastric lesions .
mucosa - associated lymphoid tissue lymphoma ( maltoma ) is a subtype of b - cell non - hodgkin 's lymphoma , comprising 17% of all gastrointestinal ( gi ) tract lymphomas . 
 it is associated with chronic inflammation and autoimmunity , for example helicobacter pylori gastritis and sjogren 's syndrome , respectively . 
 approximately 50% of gi maltomas occur in the stomach , with small bowel and colonic lesions being less frequent . 
 synchronous upper and lower gi maltomas occur rarely , with few cases reported . 
 we present the case of a 73-year - old patient who presented with change in bowel habit and was found to have synchronous multifocal upper and lower gi maltomas , which did not respond to h. pylori cure or to rituximab therapy , but did respond to a combination of surgery and chemotherapy with rituximab and bendamustine .