prostate cancer is the second most common cancer and sixth leading cause of cancer death in men worldwide . patients with prostate cancer commonly presents with urinary symptoms , bone pain , or diagnosed with raised prostate - specific antigen ( psa ) incidentally . correct staging and early diagnosis of recurrence by a precise imaging tool is what required in cancer management . cancer imaging is passing through a transition phase from morphological to molecular imaging in clinics . similarly , in prostate cancer , many newer specific molecular targets for imaging have been recently identified . prostate - specific membrane antigen ( psma ) is the preferred one among these ; however , few case reports questioning its signature to prostate cancer have been published recently . here , we present a first case report of psma expression in urothelial carcinoma mimicking prostate cancer metastasis on glu - nh - co - nh - lys-(axe)-[ga-68(hbed - cc ) ] ( ga-68 psma ) positron emission tomography - computed tomography ( pet - ct ) in a dual malignancy case . a 72-year - old male treated earlier with transurethral resection of prostate and the right open radical nephroureterectomy in 2013 for synchronous double malignancy ( high - grade invasive papillary urothelial carcinoma right ureter and adenocarcinoma prostate gleason 4 + 4 ) presented with rising psa ( 0.59 ng / ml ) with psa doubling time of < 6 months on routine follow - up . he was referred for ga-68 psma pet - ct scan to our department to localize disease recurrence site . pet - ct scan revealed psma expressing enlarged left supraclavicular lymph node measuring 4.0 cm  3.0 cm with suvmax 4.9 [ figure 1 ] and no focal tracer uptake in the prostatic fossa . in the given clinical scenario of rising psa , pet - ct finding favored recurrent prostate carcinoma . biopsy from the left supraclavicular lymph node was performed and microscopic examination revealed metastatic poorly - differentiated carcinoma with focal necrosis [ figure 2 ] . immunohistochemistry ( ihc ) examination revealed tumor cells express ck7 and gata-3 strongly and diffusely while ck20 expression was focal and moderate however negative for prostate - specific acid phosphatase ( psap ) [ figure 3 ] . ga-68 prostate - specific membrane antigen positron emission tomography - computed tomography scan , ( a ) maximum intensity projection ; ( b ) axial computed tomography ; ( c ) axial positron emission tomography ; ( d ) fused positron emission tomography - computed tomography : images show prostate - specific membrane antigen avid enlarged left supraclavicular lymphnode ( black arrow ) core biopsy from the left supraclavicular lymphnode shows a tumor embedded in a fibrous stroma . ( a ) h and e , 10 ; ( b ) : h and e , 20 ) a tumor which is positive for ck7 ( diaminobenzidine , 20 ) . ( b ) a tumor which is focally positive for ck20 ( diaminobenzidine , 20 ) . ( c ) a tumor which strongly expresses gata-3 ( diaminobenzidine , 20 ) . ( d ) a tumor which is negative for prostate - specific acid phosphatase ( diaminobenzidine , 20 ) newer tracers in molecular imaging are paving a way for more tumor - specific armamentarium ; however , a caution is required for their precision and exclusivity . psma has received a resurgence of attention after unsuccessful stories of psa and psap in molecular imaging . psma is a type ii membrane glycoprotein consisting of 750 amino acids ( 100120 kda ) , with a 19 amino acid intracellular component , a 24 amino acid intramembrane segment , and a large 707 amino acid extracellular component . psma exhibits folate hydrolase / glutamate carboxypeptidase ii enzymatic activity ; however , its precise role in vivo has not yet fully elucidated . in vitro certainly its expression is directly proportional to gleason score and hormone resistant in prostate cancer but expression can be lost in poorly - differentiated tumor cell . psma is also expressed in salivary glands , duodenal mucosa , subset of proximal renal tubular cells , and subpopulation of neuroendocrine cells in colonic crypts small intestine . silver et al . also reported that renal cell carcinoma , bladder transitional cell carcinoma , and colonic adenocarcinoma cells do not exhibits psma expression however intratumoral and peritumoral capillary endothelial cells showed intense immunoreactivity . case reports of false - positive psma pet - ct have been published in renal cell cancer , differentiated thyroid cancer , glioblastoma , breast cancer brain metastasis , and paravertebral schwannomas with expression limited to neovasculature endothelial cells in most . in our case , the patient had synchronous malignancies in the right ureter and prostate and with rising psa ( 0.59 ng / ml ) and short psa doubling time ( < 6 months ) , a more specific scan ( ga - psma ) was performed which showed positive left supraclavicular lymph node , nonetheless biopsy with ihc suggest metastatic urothelial carcinoma . gata-3 is a sensitive and specific marker for urothelial carcinoma both in primary and nodal metastasis . ck20 is also positive in half of urothelial carcinoma . because of suboptimal sensitivity of psa for high - grade prostate carcinoma , no further ihc such as psma was done due to financial constraints . in this case , most likely psma has been expressed on neovasculature of metastatic urothelial carcinoma cells and caused false - positive results on pet - ct . in our experience of over 150 cases of ga-68 psma pet - ct since 2014 , we have indeed seen psma expression in synchronous mucinous adenocarcinoma colon and metastatic lymph nodes from parotid gland carcinoma in one of each case as well . psma pet - ct has received tremendous attention in molecular imaging , especially for the diagnosis of recurrence in treated prostate cancer patients . being a very sensitive test , its use has grown in recent years despite few known limitations . this case report further highlights its vigilant use in differentiating prostate carcinoma with other solid cancers . quantification values may be a key factor for differentiating false positive from true ones and should be a topic of research for the future .
prostate cancer is the second most common cancer in man . 
 it commonly presents with urinary symptoms , bone pain , or diagnosed with elevated prostate - specific antigen.(psa ) levels . 
 correct staging and early diagnosis of recurrence by a precise imaging tool are the keys for optimum management . molecular imaging of prostate cancer with ga-68 prostate - specific membrane antigen.(psma ) , positron emission tomography - computed tomography.(pet - ct ) 
 has recently received significant attention and frequently used with a signature to prostate cancer - specific remark . 
 however , this case will highlight the more cautious use of it . 
 a-72-year - old male treated earlier for synchronous double malignancy.(invasive papillary urothelial carcinoma right ureter and carcinoma prostate ) presented with rising psa.(0.51.ng / ml ) and referred for ga-68 psma pet - ct , which showed a positive enlarged left supraclavicular lymph node . 
 lymph node biopsy microscopic and immunohistochemistry examination revealed metastatic carcinoma favoring urothelial origin . 
 specificity of psma scan to prostate cancer has been seen to be compromised in a certain situation mostly due to neoangiogenesis , and false positives emerged in renal cell cancer , differentiated thyroid cancer , glioblastoma , breast cancer brain metastasis , and paravertebral schwannomas . understanding the causes of false positive will further enhance the confidence of interpretating psma scans .