the two pathological varieties found are squamous - cell carcinoma and primary adenoid cystic carcinoma ( pacc ) though the latter accounts for less than 1% of all malignant tumors . such tumors may appear in the respiratory epithelium , the salivary glands , or in the mesenchymal tissue . therefore , they tend to occur mainly in the trachea , carina or the main or lobar bronchus . some studies have reported that patients with pacc complain of chronic symptoms and have divided them into two groups : first , those with airway obstruction who are treated for obstructive lung disease ( i.e. , asthma ) ; and , second , patients with associated lung infections . in most cases , reaching a definitive diagnosis requires a relatively long period of time because the symptoms tend to be non - specific and of extended duration ; thus most patients present forms of the disease that are already locally advanced . despite this , prognoses are good unless metastasis is documented . mexico 's national institute of respiratory diseases ( nird ) is a third - level , national reference center where the average number of hospital admissions is approximately 4000 patients per year . of those , only for the year 2009 , malignant respiratory diseases represented the third highest cause of hospitalization , with 10.5% of all cases . this study reviewed cases from 10 years of experience in this exclusive respiratory center for the purpose of ascertaining : 1 ) the frequency of pacc ; 2 ) its clinical symptoms ; 3 ) possible risk factors ; 4 ) a more complete description of the characteristic lung function of pacc patients ; and , 5 ) outcomes . this is a retrospective analysis that included all the medical charts from patients admitted to the nird consecutively with pathological diagnoses of pacc between january 1 , 2000 and december 31 , 2009 . an informed consent was not required , but all information was kept confidential and used exclusively for research purposes . the following variables were identified on the basis of a systematic review of the medical charts of the 9 cases found : age , gender , history of smoking , the tobacco index ( pack - years ) , biomass exposure ( hours / day ) , main symptoms ( cough , dyspnea , chest pain , wheezing , hemoptysis , stridor , fever and weight loss ) , average time from the onset of symptoms to diagnosis , results of radiographic evaluation ( chest x - ray , ct scan , radionuclide bone scan , and pet / ct scan ) , measurements of lung function ( post - bronchodilator spirometry and arterial blood gas analysis ) , treatment , survival time , and outcomes . all data were analyzed statistically using spss statistics software ( version 17 , spssinc , chicago ill . ) continuous data are expressed as medians with interquartile range ( iqr ) , while categorical data are described as frequencies with percentages . the median age was 41 years ( iqr 36 - 57 ) , and 67% of patients were female . the average time from the onset of symptoms to the final diagnosis was 21 months ( iqr 6 - 30 ) . the prevalence of pacc in this study population was 9 cases out of a total of 2,634 patients with lung cancer attended during the period analyzed . this represents 0.3% of cases ( 1 out of every 292 lung cancer patients ) . characteristics of tracheobronchial adenoid cystic carcinoma patients ( n = 9 ) laboratory tests performed at the time of admission highlighted the levels of hemoglobin ( 11.7 , iqr 11 - 13.2 gr / dl ) , serum albumin ( 3.6 , iqr 3 - 4.2 gr / dl ) , and the carcinoembryonic antigen ( 0.8 , iqr 0 - 3.2 ui / l ) . atelectasis was the abnormality most often reported in chest x - rays ( 56% of cases ) , while abnormal uptake on the pet / ct scan was observed in 44% of cases . radiological and lung function findings in this series ( n = 9 ) the results of lung function tests measured by spirometry and reported as the percentage of predicted values ( % p ) using ats / ers standardized reference equations were as follows : fvc showed a median of 78% p ( iqr , 51 - 112 ) and fev1 a median of 77% p ( iqr , 50 - 90 ) with an fev1/fvc ratio of 78 ( iqr , 63 - 82 ) . the primary location of tumors was the left main bronchus ( 44% of cases ) . a total of 56% of cases were classified as being in clinical stage iv ( other scores , such as karnofsky and ecog , are shown in table 3 ) . treatment consisted of chemotherapy ( cht ) , either alone or combined with surgery and/or radiation therapy ( rt ) . of the remaining patients , 22% are considered disease - free , while another 22% are currently undergoing palliative treatment for distant metastasis . location , staging and treatment of the group analyzed ( n = 9 ) characteristics of the population studied involving lung function and its association with exposure factors , anatomical location , histological type , and survival the main findings of our study were as follows : 1 ) disease frequency was low and similar to that previously reported ( 0.3% , representing 1 out of every 292 hospital discharges due to pulmonary malignancy ) ; 2 ) two - thirds of our series had previous exposure to tobacco and/or biomass fuel smoke ; 3 ) hemoptysis , wheezing , and stridor showed a lower frequency in this study population ; 4 ) a more complete description of the lung function of pacc patients ; and , 5 ) mean survival time and outcomes . our results offer important support for this finding , especially because they come from a hospital that is devoted exclusively to treating cases of respiratory disease . the mean age at presentation was also similar to that previously reported in the literature . with regards to gender prevalence , our sample had a higher number of female cases ( male to female ratio 1:2 ) . this proportion constitutes an infrequent finding because pacc has been described as having no gender predilection . however , the small number of patients included in earlier studies may account for this difference . shimizu et al . , significantly , reported the results of a recent study over a 27-year period in which all patients were female ( 100% ) . a history of smoking was documented in 67% of the cases , with a median tobacco index of 3.8 pack - years . although a relationship between tobacco use and pacc has not been described previously , it is reasonable to consider smoking as a risk factor as is the case in other strains of bronchogenic carcinoma . in addition , it is noteworthy that two - thirds of our series had prior exposure to biomass combustion ( median of 5 hours / day ) . to the best of our knowledge biomass smoke exposure seems to cause disruptions in the bronchial epithelium and can eventually cause abnormalities related to pre - malignant conditions such as those described in patients with chronic obstructive pulmonary disease ( copd ) . for these reasons , future research should explore whether tobacco use and exposure to biomass smoke might be risk factors associated with pacc . as mentioned above , the main symptoms identified were chronic coughing and dyspnea . wheezing and stridor were present in 33% of our population ; however , albers et al . have reported these clinical features in up to 50% of cases . in addition , yang et al . have reported that 71% of their cases showed hemoptysis as an initial symptom , a clue that might allow us to reach more timely diagnoses . despite the advanced clinical stages characteristic of our series , however , we observed hemoptysis in only one - third of cases . as far as we know , the results of pulmonary function tests of patients with pacc have not been published previously . thus , one of the significant findings of our series was the presence of hypoxemia . it is important to note that severe hypoxemia was present in those patients whose lung function showed serious abnormalities [ table 4 ] . taken together , these findings may explain the mechanism of hypoxemia , which is most likely due to v / q mismatches . in addition , we were able to identify that obstructive patterns were related to those patients who had a history of smoking . the overall fev1/fvc ratio was normal ( 78% p ) ; however , 3 patients had values indicating obstruction with different degrees of severity . no patient showed any response to bronchodilator use , and the flow - volume loops showed no abnormalities . with respect to this finding , it is important that the physicians who treat patients with this condition be particularly cautious with their lung function reports . it is imperative that spirometry findings be analyzed as a whole , using validated or local reference values and flow - volume loops . in this way , it may be possible to determine abnormalities , such as delays in gas - filling , and parameters capable of differentiating between intrathoracic and extrathoracic obstructions in patients with a fixed obstructive pattern that could be a clue that leads to more accurate diagnoses . also , the pulmonary function test technologist must be encouraged to obtain a maximum number of repeatable maneuvers of expiratory and inspiratory flow - volume loops , to allow the attending physician to make a correct interpretation . finally , there were cases with concomitant decreases in both fvc and fev1 , which suggest the presence of lung restriction . apparently , no specific lung function phenotype is closely related to this disease though a higher prevalence of an obstructive pattern was observed . given its level of involvement , atelectasis was the most frequent finding in x - ray imaging . we would hypothesize that these patients might have complained of wheezing in the early stages of disease development , but because of the advanced stage of the illness in our series of cases , such symptoms could have been absent or minimized by the patients general condition at the time of the initial evaluation . based on the delay in reaching diagnoses ( median evolution time with symptoms , 12 months ) , a metastatic expression of the disease was to be expected . in this regard , 60% of our patients showed a metastatic uptake on radionuclide bone scans during their initial evaluation . it is important to mention that this same frequency has been reported in other studies . due to the advanced clinical stage of disease evolution , treatment was mainly palliative . recently , a new modality of rt techniques , that includes adjuvant tomotherapy ( intensity - modulated radiation therapy ) , has been used in palliative care and appears to be of some use . in this series of cases , the frequency of pacc was low ( 0.3% ) . both , tobacco and exposure to biomass fuel smoke , appears to be an important factor . lung function tended to show an obstructive pattern ; however , additional prospective studies will have to describe lung function in greater detail including the description of the flow - volume loops , which could provide clues to the most effective diagnostic approach .
background : mexico 's national institute of respiratory diseases ( nird ) is a third - level national reference center . 
 primary adenoid cystic carcinoma ( pacc ) is an uncommon neoplastic disorder ; hence improvements in the description of this disease are needed.materials and methods : this is a retrospective clinical study based on all consecutive patients with pathological diagnoses of pacc seen at the nird between january 1 , 2000 and december 31 , 2009.results:we identified 9 cases of pacc ( 67% female ) out of a total of 2,634 patients with lung cancer seen during the period analyzed . 
 the mean age of those 9 patients was 41 years ( iqr 36 - 57 ) , and the frequency of pacc at our center was 0.3% . 
 it is important to note that 67% of those patients had a history of smoking and that 6 of the 9 had the antecedent of previous exposure to biomass fuel smoke . 
 baseline arterial blood gas analyses revealed a median of 61 mmhg for po2 and 28.5 mmhg for pco2 . 
 median fvc was 78% , while fev1 was 77% with an fev1 /fvc ratio of 78 . 
 death occurred in 56% of cases , and the median survival time was 17 months ( iqr 6 - 26 ) after the initial diagnosis.conclusions:the frequency of tracheobronchial pacc among patients with lung cancer was similar to that previously reported ( 0.3% ) . according to our results 
 , lung function has no specific phenotype in this disease ; however , some abnormalities could be related to potential risk factors such as tobacco use and exposure to biomass fuel smoke .