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:
we selected 107 cases of pulmonary adenocarcinoma diagnosed at samsung medical center and gachon university gil medical center between march 2010 and july 2012 .
all tumors , except one , were collected using endobronchial - ultrasound guided biopsy ( ebus ) . in 15 cases ,
the 15 cases were diagnosed by biopsy , and examined by immunohistochemistry using alk protein ( 1:40 , clone 5a4 , novocastra , newcastle upon tyne , uk ) .
eml4-alk rearrangements were confirmed in all alk - positive immunoreactive cases by fish analysis using an alk break - apart probe ( vysis lsi alk dual color , break - apart rearrangement probe , abbott molecular , abbott park , il , usa ) .
fine needle aspiration cytologies from the 16 cases of alk - negative pulmonary adenocarcinoma were also evaluated .
scoring was as follows : 0 , no evidence of cytologic features ; 1 , < 30% of cytologic features in smeared slides ; 2 , 30% of cytologic features in smeared slides .
each cytologic smear was evaluated for the following features : 1 ) background pattern , mucin , hemorrhage , and necrosis ; 2 ) cellular arrangement , such as tubulopapillary , tubulocribriform , acini , sheet , cluster , and single ; 3 ) individual cell morphology such as vesicular nuclei , presence of nucleoli , dense chromatin , and signet ring cell features . '
histologic sections were assessed for histologic patterns ( solid , micropapillary , acinar , lepidic , mucinous , and signet ring cells scored as two parts : < 10% , 10% ) and nuclear grade ( i , ii , iii ) .
we used the chi - square test to evaluate the differences in cytologic features between alk - positive adenocarcinomas and alk - negative adenocarcinomas .
fisher exact test was used instead of the chi - square test in cases in which 50% of the cells had expected counts of less than 5 .
we selected 107 cases of pulmonary adenocarcinoma diagnosed at samsung medical center and gachon university gil medical center between march 2010 and july 2012 .
all tumors , except one , were collected using endobronchial - ultrasound guided biopsy ( ebus ) . in 15 cases ,
the 15 cases were diagnosed by biopsy , and examined by immunohistochemistry using alk protein ( 1:40 , clone 5a4 , novocastra , newcastle upon tyne , uk ) .
eml4-alk rearrangements were confirmed in all alk - positive immunoreactive cases by fish analysis using an alk break - apart probe ( vysis lsi alk dual color , break - apart rearrangement probe , abbott molecular , abbott park , il , usa ) .
fine needle aspiration cytologies from the 16 cases of alk - negative pulmonary adenocarcinoma were also evaluated .
scoring was as follows : 0 , no evidence of cytologic features ; 1 , < 30% of cytologic features in smeared slides ; 2 , 30% of cytologic features in smeared slides .
each cytologic smear was evaluated for the following features : 1 ) background pattern , mucin , hemorrhage , and necrosis ; 2 ) cellular arrangement , such as tubulopapillary , tubulocribriform , acini , sheet , cluster , and single ; 3 ) individual cell morphology such as vesicular nuclei , presence of nucleoli , dense chromatin , and signet ring cell features . '
histologic sections were assessed for histologic patterns ( solid , micropapillary , acinar , lepidic , mucinous , and signet ring cells scored as two parts : < 10% , 10% ) and nuclear grade ( i , ii , iii ) .
we used the chi - square test to evaluate the differences in cytologic features between alk - positive adenocarcinomas and alk - negative adenocarcinomas .
fisher exact test was used instead of the chi - square test in cases in which 50% of the cells had expected counts of less than 5 .
the patients ranged in age from 25 to 67 years ( mean age , 52 years ) .
most ebuss of alk - positive adenocarcinomas showed mucinous ( 13/16 , 81.3% ) , hemorrhagic ( 8/16 , 50.0% ) , and necrotic ( 3/16 , 18.8% ) backgrounds .
an extensive mucinous background was observed in two cases , and 11 cases were focally mucinous admixed with tumor cells .
these contained cellular aspirates , even though they were less cellular than fine needle aspiration cytology .
the tumor cells were arranged in sheets ( 15/16 , 93.8% ) , clusters ( 9/16 , 56.3% ) , and single cells ( 11/16 , 68.8% ) .
the clusters were relatively loose and the sheets were somewhat tubulopapillary or tubulocribriform in appearance ( p<0.001 ) ( fig .
the scattered single cells showed vesicular nuclei ( 14/16 , 87.5% ; p<0.001 ) and signet ring cell features ( 14/16 , 87.5% ; p<0.001 ) ( fig .
the nuclei had an open chromatin appearance - similar to the nuclei of papillary carcinoma of the thyroid ( ground glass appearance ) .
the single cells had the appearance of small histiocyte - like cells and sometimes also contained intracytoplasmic mucin vacuoles .
large prominent nucleoli were observed in two cases ( 2/16 , 12.5% ) ( fig .
a summary of the cytological features of 16 cases is shown in table 1 . when the cytologic features were scored , a high score ( more than 2 ) was found to be associated with a single cell pattern ( four cases ) , a signet ring cell pattern ( six cases ) , and significant mucinous background ( two cases ) .
the cellularity and background of alk - negative pulmonary adenocarcinomas showed : cells were in loosely cohesive groups , syncytial tissue fragments , acini ( 13/16 , 81.3% ) , and tubule .
cytoplasms were pale to dense , foamy , or lacy containing small several intracytoplasmic vacuoles , not single vacuoles .
the nuclei displayed relatively uniform , smooth to irregular nuclear membranes with small to large prominent nucleoli , that were larger compared with those of alk - positive adenocarcinomas .
the specificity of the tubulopapillary or tubulocribriform patterns and the vesicular chromatin in cytologic smears to predict for alk - positive adenocarcinoma was 81.3% .
those of signet ring cell morphology and single cell distribution were 93.8% and 81.3% , respectively .
those of signet ring cell morphology and single cell distribution were 87.5% and 68.8% , respectively .
in histologic findings , backgrounds were hemorrhagic ( 8/16 , 50.0% ) , mucinous ( 4/16 , 25.0% ) , and necrotic ( 0/16 , 0% ) .
eight ( 50.0% ) cases showed a cribriform formation with a rigid or flaccid appearance .
individual signet ring cells were identified in 14 ( 87.5% ) cases , accounting for 0% of tumor cellularity ( 2/16 , 12.5% ) , < 10% ( 7/16 , 43.8% ) , and 10% ( 7/16 , 43.8% ) ( fig .
molecular targeted therapy has played an increasingly important role in cancer treatment , particularly in genetically defined subsets of patients .
alk gene rearrangements in nsclc carcinogenesis were first reported in 2007.14 the eml4-alk fusion gene has been identified in 1 - 5% of cases of nsclcs.2,8 - 11 alk inhibitors have been developed and have shown effective activity in alk - rearranged nsclcs .
the histologic findings of alk - rearranged nsclcs included an acinar growth pattern , extracellular mucus production , and signet - ring cell morphologies in associated with solid growth.9 - 12 some researchers have reported findings of solid or acinar growth patterns , cribriform structure , presence of mucous cells ( signet ring cells or goblet cells ) , abundant extracellular mucus , lack of lepidic growth , and lack of a significant nuclear pleomorphism . in particular , a combination of two findings , such as a solid signet ring cell pattern and a mucinous cribriform pattern , were observed in the majority of alk - positive tumors.15 in this study , most cytologic smears of alk - positive adenocarcinomas showed mucinous background ( 81.3% ) , even though it was focal , not extensive , except in two cases . other backgrounds , such as hemorrhage ( 50.0% ) and necrosis ( 18.8% ) , might be nonspecific for malignant tumors .
the background of alk - negative adenocarcinoma was variable , rather than specific as with malignant tumors .
the majority of cells of alk - positive tumors were arranged in sheets with tubulopapillary or tubulocribriform patterns ( 93.8% ) .
however acinus pattern was also found to be significant on statistical analysis , and was relatively frequently observed for glandular forming adenocarcinoma and therefore might be an unspecific feature .
cluster formation showed a relatively loose arrangement ( 56.3% ) , however clusters contained cells having mucous vacuoles ( goblet - cell - like feature ) .
scattered signet ring cells , goblet - like cells , or mucous cells , were found in 87.5% of cases ( p<0.001 ) .
song et al.16 suggested that the histologic findings of adenocarcinomas expressing alk show intra- and extra - cytoplasmic mucin and show a signet ring cell appearance , or a cribriform pattern with extracytoplasmic mucin.16 these histologic findings are compatible with cytologic features .
these findings were reminiscent of alk - rearranged anaplastic large cell lymphoma , which tends to show less nuclear pleomorphism than the alk - wild type variety.17 the specificity and sensitivity of the tubulopapillary or tubulocribriform patterns and vesicular chromatin in cytologic smears to predict alk - positive adenocarcinoma were higher than those of other cytologic findings .
however there were only 16 cases of alk - positive adenocarcinoma , it will be necessary to study a larger group .
the morphologic criteria of fine needle aspiration cytology for classic adenocarcinoma include small aggregates with glandular , acinar , and papillary architecture .
the cell membrane is poorly defined , and cells show scanty and vacuolated cytoplasm with prominent nucleoli.18 the differences in features between classic adenocarcinoma ( alk - negative adenocarcinoma ) and alk - positive adenocarcinoma are cell architecture ( tubulopapillary , tubulocribriform , and scattered single cells ) and in chromatin pattern ( vesicular and bland , and small tiny nucleoli ) . based on the specificity and sensitivity findings , the specific cytological findings to predict alk - positive adenocarcinoma might be tubulopapillary or tubulocribriform architectures , signet ring cells , and vesicular chromatin .
one of the cytologic features of mucinous adenocarcinoma is the presence of abundant extracellular mucin admixed with a variable number of neoplastic cells , histiocytes , multinucleated giant cells , fibroblasts , and stromal fragments.19 the tumor cells showed sharply delineated cell borders and unevenly distributed nuclei , forming a characteristic " drunken honeycomb " pattern with tall columnar cells.20 on the other hand , alk - positive adenocarcinoma frequently showed a relatively small amount of mucin , and did not have tall columnar cells .
however , that of mucinous adenocarcinoma was slightly irregular . a lepidic pattern in pulmonary adenocarcinoma tends to exfoliate as single cells , papillary fronds , and sheets .
the nuclei are characteristically round to oval and uniform in size , with finely granular or powdery chromatin and inconspicuous nucleoli .
alk - positive adenocarcinoma had similar nuclear features of a lepidic pattern.20 the tumor cells were arranged in a tubulopapillary or tubulocribriform pattern and had small nucleoli . scattered single cells were more common in the fields of cytologic smears . making a differential diagnosis may be difficult , however there are several morphological features that can help provide a diagnosis . in conclusion , a tubulopapillary or tubulocribriform arrangement and scattered single monotonous cells ( signet ring cell ) with uniform vesicular nuclei
these finding might not be definitive ; however , they are helpful in suggesting a diagnosis .
backgroundthe aim of this study was to determine the cytologic features of anaplastic lymphoma kinase ( alk ) expressing pulmonary adenocarcinoma.methodswe analyzed the cytopathological 
 findings of 15 cases of endobronchial ultrasound guided aspiration and a case of bronchial washing . 
 these cases were selected based on the histomorphology of alk - rearranged lung adenocarcinoma.resultscytology showed mucinous ( 81.3% ) and hemorrhagic ( 50% ) backgrounds . 
 the cells were arranged in tubulopapillary or tubulocribriform patterns ( 93.8% ) , and clusters ( 56.3% ) admixed with signet ring cell features ( 87.5% ) . 
 the tumor cells were monotonous and uniform with vesicular nuclei and a small nucleolus.conclusionsthe characteristic findings were sheets showing a tubulopapillary or tubulocribriform appearance , with vesicular nuclei and a bland chromatin pattern ( p<0.001 ) . 
 scattered signet ring cells were helpful in suggesting alk - positive adenocarcinoma ( p<0.001 ) .