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:
primary mediastinal large b - cell lymphoma ( pmlbcl ) is one of the subtypes of diffuse large b - cell lymphoma ( dlbcl ) , which is derived from b cells of thymic origin ( 1 - 4 ) .
it usually occurs in young women and presents as a rapidly enlarging anterior mediastinal mass .
the most common symptoms of the disease including coughing , chest pain , dyspnea , and venous obstruction . recently
, endobronchial ultrasound - guided transbronchial needle aspiration ( ebus - tbna ) has been reported to be useful for investigating cases of suspected lymphoma ( 5 ) ; however , pmlbcl are rarely directly observable during endoscopy .
we herein present the case of a young woman with pmlbcl , in which an endobronchial tumor was directly observed and diagnosed by bronchoscopy .
a 33-year - old japanese female with the chief complaints of epigastralgia , back pain , and nausea visited a primary care hospital .
in addition to her chief complaints , the patient had also been suffering from a cough , general malaise , and loss of appetite for a month .
computed tomography ( ct ) of the chest and abdomen demonstrated a bulky mass measuring 10 cm in diameter in the left anterior mediastinum , multiple pulmonary nodules ( measuring up to 3 cm in diameter ) , axillary lymph node swelling ( fig .
1 ) , and a pancreatic tumor . she was therefore admitted to our hospital for further examination and symptom management .
the patient 's physical findings at the time of the first medical examination were as follows : pulse rate : 72/min ( regular pulse ) , blood pressure : 128/80 mmhg , body temperature : 36.7 , and oxygen saturation ( spo2 ) : 97% in room air .
serological tests revealed the following findings : c - reactive protein level : 5.24 mg / dl , lactate dehydrogenase level : 979 iu / l , fibrinogen level : 509 mg / dl , d - dimer level : 1.8 g / ml , and fibrin degradation product level : 9.19 g / ml . tumor marker tests detected elevated soluble interleukin-2 receptor ( 1,660 u / ml ) levels . computed tomographic images of the chest with the mediastinal ( a , b ) and lung window settings ( c ) obtained at onset .
fiberoptic bronchoscopy revealed a white - tinged irregularly shaped endobronchial tumor accompanied by capillary vessel dilatation in the left upper lobar bronchus , which was found to be almost completely obstructed ( fig .
2 ) . a histological examination detected bright cell bodies of various sizes and tumor cells with naked nuclei .
the cells exhibited a proliferative and invasive activity , but they had not yet formed a well - defined structure ( fig .
3 ) , and an immunohistochemical examination showed the tumor cells to be negative for cd3 ( fig .
4a ) , cd56 , synaptophysin , and ae1/ae3 ( data not shown ) , while they were positive for cd20 ( fig .
histologically , the tumor was diagnosed to be diffuse large b - cell lymphoma , and as the primary tumor developed in the mediastinum we finally diagnosed the patient with pmlbcl .
the patient was treated with r - chase ( rituximab , cyclophosphamide , high - dose arabinoside , steroids , and etoposide ) chemotherapy and achieved a tumor response ( fig .
tumor marker tests also detected normalized soluble interleukin-2 receptor ( 314 u / ml ) levels .
pathological features observed during an immunohistochemical examination of the cd3 ( a ) and cd20 ( b ) expression .
computed tomographic images of the chest with the mediastinal ( a ) and lung window settings ( b ) obtained after one cycle of r - chase treatment .
pmlbcl was first described in the early 1980s ( 6,7 ) and is one of the subtypes of dlbcl .
it constitutes from 2 - 3% of all non - hodgkin 's lymphomas and from 6 - 10% of all dlbcl ( 1 - 4 ) .
it commonly presents as a bulky lesion in the anterior - superior mediastinum and is associated with symptoms related to local invasion or compression , including dyspnea , coughing , chest pain , and dysphagia ( 8,9 ) .
it tends to occur in younger adults and exhibits a female predominance ( median age : 30 to 40 years ; male to female ratio : 1:2 ) . in the present case ,
the patient was in her 30s and presented with a bulky mediastinal mass and anterior and back pain , coughing , dyspnea , nausea , and fatigue .
fluoroscopy- or computed tomography - guided needle biopsies often yield sufficient amounts of tissue specimens for a diagnostic workup and to prepare paraffin - fixed tissue sections for histological examinations and immunohistochemical analyses ( 4 ) . recently , ebus - tbna was reported to be useful for diagnosing primary mediastinal malignant lymphoma ( 9,10 ) . in the present case ,
fiberoptic bronchoscopy detected endobronchial involvement , and we were able to obtain tumor samples from the lingular segment of the left lung and thus diagnose pmlbcl without ebus - tbna .
the development of extrapulmonary malignant tumors in the endobronchial region is uncommon and is mainly associated with colon , breast , and kidney cancer ( 11,12 ) . although lymphomas often occur in the lungs , endobronchial lymphoma is extremely rare , and very few of the cases reported in the literature were diagnosed by bronchoscopy .
for example , no endobronchial lesions were detected in a study of 55 patients who were diagnosed with non - hodgkin 's lymphoma ( 13 ) , and only one endobronchial lesion was seen among 93 patients with primary lung lymphoma ( 14 ) .
the first involves the accumulation of diffuse submucosal infiltrates due to the lymphangitic or hematogenous spread of systemic lymphoma such as colon , breast and lung cancer .
the other type , to which the present case belongs , involves the development of a localized nodule in the airway due to the direct spread of lymphoma from the neighboring lymph nodes or the de novo development of such a lesion from bronchus - associated lymphoid tissue .
bronchoscopy or ebus - tbna should be performed to screen for endobronchial involvement in cases involving a mediastinal mass and multiple pulmonary nodules .
the optimum chemotherapy regimen for pmlbcl has not yet been established , and several approaches from first - generation cyclophosphamide ( chop)-like regimens to third - generation multi - drug chemotherapy regimens have been tried ( 15 ) . in the present case ,
the patient was treated with the r - chase regimen and achieved a partial response .
r - chase is a combination chemotherapy regimen in which rituximab is added to the chase regimen ( cyclophosphamide , cytosine arabinoside , etoposide , and dexamethasone ) developed by the aichi cancer center ( 16 ) . in a pilot phase
i / ii study of patients with refractory or relapsed lymphoma , the chase regimen achieved a complete response rate of 71.4% in 14 patients .
recently , dunleavy et al . administered the dose - adjusted etoposide , doxorubicin , and cyclophosphamide with vincristine , prednisone , and rituximab ( da - epoch - r ) regimen in combination with filgrastim ( without radiotherapy ) and achieved an event - free survival rate of 93% and an overall survival rate of 97% during a median follow - up period of 5 years ( 17 ) .
, we herein reported a case of pmlbcl exhibiting endobronchial involvement , in which the disease was diagnosed by bronchoscopy and treated with r - chase .
although endobronchial pmlbcl lesions are rare , we consider that bronchoscopy should be promptly performed when a mediastinal mass and pulmonary lesions are observed on ct .
primary mediastinal large b - cell lymphoma ( pmlbcl ) is one of the subtypes of diffuse large b - cell lymphoma . 
 we experienced a rare case of pmlbcl that exhibited endobronchial involvement . 
 a 33-year - old japanese female with the chief complaints of epigastralgia , back pain , and nausea visited a primary care hospital . computed tomography of the chest and abdomen demonstrated a bulky mass in the left anterior mediastinum , multiple pulmonary nodules , axillary lymph node swelling , and a pancreatic tumor . 
 fiberoptic bronchoscopy showed a white - tinged irregularly shaped endobronchial tumor accompanied by capillary vessel dilation in the left upper lobar bronchus . 
 taken together , these findings resulted in a diagnosis of pmlbcl .