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a 67-year - old female presented to the emergency room with abdominal pain secondary to diverticulitis and was found to have a large left renal mass .
the patient 's medical history was significant for hyperlipidemia and diverticulitis ; however , there was no past or family medical history of urologic malignancies .
an abdominal computed tomography ( ct ) scan revealed an infiltrative mass arising from the upper pole of the left kidney , which was suggestive of rcc . a ct scan of the chest demonstrated punctate lung nodules of indeterminate significance .
there was no evidence of extrarenal tumor involvement noted at the time of the procedure .
the radical nephrectomy specimen was routinely fixed in 10% buffered formalin , embedded in paraffin , and serially sectioned into 4-m - thick sections .
immunohistochemical staining was performed using the avidin - biotin - peroxidase complex method in a dako autostainer ( dako , carpinteria , ca ) with standard techniques .
primary antibodies included cd10 , pax-8 , vimentin , alpha - methyl - coa racemase ( amacr ) , pin dual stain ( cocktail of high molecular weight cytokeratin and p63 ) , thrombomodulin , ulex europaeus lectin , cytokeratin 7 ( ck7 ) , and cytokeratin 20 ( ck20 ) .
the nephrectomy specimen showed a 6.0 cm  6.0 cm  4.0 cm poorly circumscribed tumor in the upper pole of the kidney .
approximately 70% of the tumor cut surface was solid , fibrous tan - white , and 30% of that was soft , lobulated tan - yellow with focal areas of hemorrhage within the soft tan - yellow areas ( figure 1 ) .
the first was a clear cell rcc , which corresponded to the bright yellow areas grossly identified within the tumor .
the tumor cells in these foci were of low nuclear grade ( fuhrman nuclear grade 2 ) .
the second component , which comprised the majority of the tumor , corresponded to the white fibrotic areas within the tumor and was composed of a high - grade tumor with glandular / tubular differentiation ( figures 2a  c ) .
this tumor was of high nuclear grade ( fuhrman nuclear grade 4 ) and was associated with extracellular mucin production and extensive desmoplastic stroma .
another unusual finding was the presence of extensive perineural invasion in this area , a feature that is rarely noted in renal tumors , as well as the presence of hyaline globules noted within the high - grade component .
immunohistochemical stains revealed that the clear cell component was positive for cd10 , pax-8 , vimentin , and amacr ( p504s ) and negative for pin dual , thrombomodulin , ulex europaeus lectin , ck7 , and ck20 .
the high - grade component was positive for cd10 , pax-8 , vimentin , ulex europaeus lectin , and ck7 ; focally positive for amacr ; and negative for pin dual , thrombomodulin , and ck20 ( figure 3 ) .
although urothelial carcinoma was considered in the differential diagnosis , the lack of an in situ urothelial carcinoma component , coupled with the strong expression of pax-8 , vimentin , and ulex europaeus lectin and the negative staining for pin dual ( cocktail of high molecular weight cytokeratin and p63 ) , helped bolster the diagnosis of collecting duct carcinoma . the histologic features and immunohistochemical profile of the higher - grade component were consistent with collecting duct carcinoma . due to the close proximity of the two components , along with the presence of both the clear cell and the collecting duct carcinoma components at the interface ,
the tumor was best thought to represent a collision tumor , composed of clear cell rcc and collecting duct carcinoma .
a fine needle aspiration of the lung showed numerous three - dimensional cell clusters and papillary groups .
as in the primary renal tumor , intracellular and extracellular hyaline globules were present , seen especially on cell block sections .
the findings were consistent with metastasis from the collecting duct carcinoma component of the primary renal tumor .
there were no cells with features of clear cell carcinoma ( figures 2d  e ) .
the majority of the tumor is gray - white and fibrotic and demonstrates collecting duct morphology ( notched red arrow ) .
also identified is a soft yellow area that appears to be somewhat sharply demarcated from the above mentioned component , which histologically demonstrates clear cell histology ( solid blue arrow ) .
a , low power image demonstrates a sharp demarcation between the collecting duct carcinoma ( top right ) and clear cell carcinoma ( bottom left ) .
b , high power image demonstrates the low fuhrman nuclear grade clear cell renal cell carcinoma component .
c , the collecting duct carcinoma component is composed of a high - grade tumor with prominent glandular features .
d , fine needle aspiration specimen from the lung metastasis demonstrates high - grade carcinoma .
e , cell block preparation demonstrates high - grade carcinoma with histologic features similar to the renal collecting duct carcinoma . also noted within the aspiration specimen
the patient had a clinical response , with decreased pain and improved performance status , and stable radiographic findings .
after four cycles of treatment with paclitaxel and carboplatinum , she developed neuropathy necessitating a change of therapy and then proceeded to undergo doxorubicin and gemcitabine .
she then developed clinical evidence of soft tissue and bone metastasis in the thoracic spine , for which she underwent radiation treatment . despite undergoing treatment
collision tumors arising in the kidney are unusual , with only a handful of cases documented thus far in the literature .
the reported cases of renal collision tumors have included collecting duct carcinoma arising in conjunction with chromophobe rcc , or papillary rcc. other reported tumor combinations have included chromophobe rcc and oncocytoma arising in association with papillary rcc. cho et al . reported a case of collision tumor of the kidney where the dominant tumor mass resembled a clear cell rcc .
the tumor reportedly also demonstrated a smaller nodule with a tubulopapillary architecture that was felt to morphologically resemble a collecting duct carcinoma , despite the reported lack of immunohistochemical support ( negative ck7 , negative ulex europaeus lectin ) .
our case , in contrast , showed typical morphology ( high - grade tubulopapillary carcinoma with a desmoplastic stroma , juxtaposed with a low - grade clear cell component ) as well as immunohistochemical characteristics of collecting duct carcinoma ( strong expression of pax-8 , vimentin , and ulex europaeus lectin and negative staining for pin dual and thrombomodulin ) in the high - grade component of the tumor .
a , c , and e demonstrate the collecting duct carcinoma are strongly positive for ck7 , ulex europaeus lectin , and pax-8 , respectively .
the clear cell carcinoma is negative for ck7 ( b ) and ulex europaeus lectin ( d ) and is positive for pax-8 ( f ) .
the existing theories include ( a ) two unrelated existing cell lines that simultaneously proliferate , thus resulting in two phenotypically different tumors ; ( b ) tumors arising from a common precursor stem cell , which differentiates along two different lines into two unrelated neoplasms , and ( c ) incidental occurrence of two different isolated tumors within a common anatomic site . because the two tumor types noted in this renal tumor had origins in the renal cortex ( clear cell carcinoma ) and the distal collecting duct ( collecting duct carcinoma ) , any of the above theories may be applicable to our case , although the close proximity and abrupt transition between the two tumor types noted both grossly and microscopically may lend credence to the former two theories .
our patient developed disease progression , with bilateral pulmonary metastasis appearing within a few months after nephrectomy .
her clinical course was thought to be more consistent with collecting duct carcinoma rather than low - grade clear cell carcinoma , which was the second component in the primary tumor .
this clinical impression was further confirmed by the findings in the fine needle aspirate specimen from the lung , which was histologically identical to that seen in the primary tumor . as has been previously reported , cytotoxic chemotherapy , including the combination of paclitaxel and carboplatinum , may provide palliation in some patients with collecting duct carcinoma .
however , the role of targeted therapy in this disease has not been defined . in summary , although rare , collision tumors composed of more than one tumor type are well documented in the kidney .
careful gross examination is invaluable ; close attention must be paid to areas that look grossly different to exclude the possibility of more than one tumor type existing in the same specimen , as prognosis is usually determined by the high - grade component .
we report the case of a 67-year - old female who presented with a large renal mass 
 . gross examination of the nephrectomy specimen demonstrated a 6-cm renal mass that invaded into the renal sinus and perinephric fat . 
 histologic examination revealed two distinct tumor types . 
 the first type was a conventional ( clear cell ) renal cell carcinoma that was of low nuclear grade and comprised the minority of the overall tumor . 
 the second type was a high - grade collecting duct carcinoma with glandular / tubular differentiation and composed the majority of the tumor . 
 immunohistochemical studies demonstrated distinctive patterns of the two tumor types , thus confirming two distinct lineages . 
 five months postoperatively , the patient developed metastasis to the lungs and right hilar lymph node region . 
 a fine needle aspiration of a lung nodule demonstrated a metastatic , poorly differentiated carcinoma , similar to the collecting duct carcinoma component in the kidney . 
 collision tumors of the kidney are rare with fewer than 10 cases reported in the literature . 
 our report further expands the spectrum of this rare phenomenon .