all the patients aged 18 and above with a histopathologic diagnosis of pulmonary scc between may 12 , 2012 and may 13 , 2013 at our medical center were identified retrospectively from the pathology database . the midline of each lung in the axial ct scan views was used as a definition point , the tumors medial to the midline were classified as being centrally located , and those lateral to the midline were classified as peripherally located tumors . of the 56 patients , demographic information of all the 56 patients , as well as other pertinent information including smoking history , inhaled steroid use , and proton pump inhibitor ( ppi ) use , was collected and described . student 's t - test was used to compare the means for the ages of the two study groups , and a chi - square test was used to compare the rest of the demographic features and risk factors mentioned above . a p - value of < 0.05 was used for all the analyzed data . all the patients aged 18 and above with a histopathologic diagnosis of pulmonary scc between may 12 , 2012 and may 13 , 2013 at our medical center were identified retrospectively from the pathology database . the midline of each lung in the axial ct scan views was used as a definition point , the tumors medial to the midline were classified as being centrally located , and those lateral to the midline were classified as peripherally located tumors . of the 56 patients , demographic information of all the 56 patients , as well as other pertinent information including smoking history , inhaled steroid use , and proton pump inhibitor ( ppi ) use , was collected and described . student 's t - test was used to compare the means for the ages of the two study groups , and a chi - square test was used to compare the rest of the demographic features and risk factors mentioned above . from may 12 , 2012 , through may 13 , 2013 , a total of 56 patients with new diagnosis of scc were identified . of them , 44.6% ( n=25 ) were found to have tumors arising from the center , and the rest 55.4% ( n=31 ) had tumors arising from the periphery of the lungs ( table 1 ) . student 's t - test was used to compare the means for the ages of the two study groups , and a chi - square test was used to compare the rest of the demographic features and risk factors mentioned above . a p - value of < 0.05 was used for all the analyzed data . we also analyzed a subgroup with no prior history of any malignancy , and a total of 29 patients were included in this subset . of the 29 patients , 37.9% ( n=11 ) were found to have centrally located tumors , and the rest 62.1% ( n=18 ) were found to have tumors arising from the periphery . the mean age was 68 ( 6.73 ) for the patients with central tumors , whereas the mean age was 69 ( 8.36 ) for the patients with peripheral tumors , and no statistically significant difference was found on the t - test . the rest of the variables including gender , race , smoking status , ppi use , and inhaled steroid use were analyzed in the subset of patients without previous history of malignancy , and no significant difference was found as well ( table 2 ) . 
 de novo subgroup analysis we also analyzed a subgroup with no prior history of any malignancy , and a total of 29 patients were included in this subset . of the 29 patients , 37.9% ( n=11 ) were found to have centrally located tumors , and the rest 62.1% ( n=18 ) were found to have tumors arising from the periphery . the mean age was 68 ( 6.73 ) for the patients with central tumors , whereas the mean age was 69 ( 8.36 ) for the patients with peripheral tumors , and no statistically significant difference was found on the t - test . the rest of the variables including gender , race , smoking status , ppi use , and inhaled steroid use were analyzed in the subset of patients without previous history of malignancy , and no significant difference was found as well ( table 2 ) . 
 de novo subgroup analysis lung cancer is the leading cause of cancer - related death among both men and women in the united states , of which sccs account for a significant proportion . traditionally , sccs of the lung have been believed to arise from the central airways , with the prevalence of peripheral scc among all scc has been reported to range from 15 to 30% ( 8 , 9 ) . but recently , a few reports have documented a change in this distribution ( 4 , 10 , 11 ) with the peripheral form of scc accounting for nearly 50% of scc of the lung . we found in our study that the peripheral scc accounted for 55% of the scc in the entire study population and for 62% in the new lung cancer subgroup . finally , most of the study patients were caucasians with a minor representation from african american and other races , and as a consequence , the results may not be generalizable . despite the limitations , our study correlates with the recent reports of increasing number of peripherally arising squamous cell cancers of the lung . though we looked at some of the demographic variables and other factors that may be influencing this change in distribution , we were unable to identify a causative factor for this shift . as these two forms of scc have considerable differences in clinicopathologic features and presentation , we believe larger prospective studies are needed to further delineate the causative factors for this change in distribution . the authors have not received any funding or benefits from industry or elsewhere to conduct this study .
backgroundtraditionally , squamous cell carcinoma ( scc ) of the lung is a central rather than a peripheral form of lung cancer . 
 rates of scc in the lung periphery are typically sited in the 1530% range . 
 recently , we observed that a significant portion of newly diagnosed scc was located on a periphery . 
 a comprehensive review of the tumor data at our facility , a busy teaching hospital with a large cohort of cancer patients , was undertaken to assess whether there had been a substantive change in the traditional epidemiologic distributions of the lung cancer , specifically with respect to scc . given the differences in cell biology and carcinogenesis of central versus peripheral scc , a potential epidemiologic shift might suggest a change in tumor biology.methodsfrom may 12 , 2012 through may 13 , 2013 , all histopathologically confirmed diagnoses of scc of the lung were retrospectively reviewed . 
 each patient 's lesion was then classified as peripheral or central based on ct evidence.resultsa total of 56 patients were diagnosed with scc . of these , 
 55% ( n=31 ) had peripheral and 45% ( n=25 ) had central scc . 
 twenty - nine patients did not have any prior history of malignancy . of this subset of patients , 
 62% ( n=18 ) had peripheral scc , and 38% ( n=11 ) had central scc.conclusionour findings appear to correlate with our initial observation that , within our institution , there has been a substantive shift in the traditional distribution of scc with the majority of these cancers now being diagnosed in the lung periphery as opposed to the more central locations .