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:
prostatic stromal sarcoma ( pss ) is quite rare , accounting for only 0.1% to 0.2% of all prostate cancers . in 1998
gaudin et al .   grouped sarcoma and related proliferative lesions of the specialized prostatic stroma into two clinicopathologic categories : prostatic stromal proliferation of uncertain malignant potential ( pspump ) and pss .
we recently experienced two cases of pss that were surgically treated by use of robot - assisted laparoscopic radical prostatectomy ( ralp ) and open radical cysto - prostatectomy with an ileal conduit .
a 29-year - old man was referred from another urologic clinic for severe perineal pain with a weak urine stream and dysuria .
when he visited kyungpook national university medical center , he reported a history of acute urinary retention and had a foley catheter in place for about 1 month .
a digital rectal examination ( dre ) showed a relatively enlarged prostate with tenderness on pressure .
an abdominal computed tomography ( ct ) scan revealed an 874.5-cm - sized moderately enlarged prostate .
the estimated volume of the prostate by transrectal ultrasound ( trus ) and the prostate - specific antigen ( psa ) level were 80 ml and 8.0 ng / ml , respectively .
considering the relatively young age of the patient , acute bacterial prostatitis was suspected , but the patient 's clinical symptoms did not exactly line up with acute bacterial prostatitis . to relieve the patient 's symptoms and drain the urine
, we performed a suprapubic cystostomy and started the patient on intravenous antibiotics , but his symptoms were not relieved .
repeated trus and dre suggested a prostate cold abscess , but prostate malignancy could not be ruled out .
the prostate mri showed a huge prostatic mass that obstructed the bladder neck ( fig .
1 ) . according to the results of the mri , we performed transurethral resection of the prostate ( turp ) to relieve the bladder outlet obstruction and to confirm the pathologic nature of the mass . the pathology report from turp indicated high - grade sarcoma with extensive necrosis .
we performed chest ct and a whole - body bone scan to evaluate the extensiveness of the disease to determine the feasibility of surgery .
no metastatic lesions were found on the chest ct or whole - body bone scan . in the prostate mri , the whole prostate was shown to be involved by the malignant lesion and rectal wall invasion was suspected .
considering the particularly young age of the patient and the lack of evidence of bladder invasion , we decided to perform ralp and extended pelvic lymph node dissection , with an expectation of sparing the bladder .
this decision was made with the informed consent of the patient and the patient 's legal guardian . during the operation , rectal wall invasion of sarcoma was noted .
gross examination of the radical prostatectomy specimen showed a 128.07.0-cm - sized relatively well - demarcated mass containing hemorrhage .
the rectal mucosa and prostatic resection margins were positive for tumor , but none of the lymph nodes had tumor present ( fig .
the patient 's symptoms and the recurred mass in the pelvis became aggravated at 45 days after the operation .
a 45-year - old man was referred from another urology clinic for voiding difficulty lasting about 2 months .
he had a history of gross hematuria and hematospermia lasting for 7 months until the present .
an abdominal ct scan revealed a 10126.4-cm - sized huge solid mass with focal cystic change in the pelvic cavity that was displacing the right ureter and with periprostatic fat infiltration and probable invasion into the urinary bladder , seminal vesicle , and rectum ( fig .
his estimated volume of the prostate by trus and his psa level were 575 ml and 1.19 ng / ml , respectively .
trus - guided prostate biopsy was performed to determine the nature of the tumor , which was revealed as a malignant spindle cell tumor with rhabdoid features , most likely pss .
we performed chest ct and a bone scan to determine the stage of the tumor and whether it had metastasized to other organs .
the chest ct and bone scan revealed no metastasis . considering the patient 's age and the aggressiveness of the disease
, open radical cysto - prostatectomy with an ileal conduit was performed . during the operation , rectal wall invasion of the sarcoma
gross examination of the radical cysto - prostatectomy specimen showed a 108.56.0-cm - sized prostate containing a bright yellow friable soft mass with central necrosis and a 9.06.05.0-cm - sized bladder with grossly noted pss invasion .
the final histopathologic analysis revealed pss with invasion to both seminal vesicles and the subserosal layer of the rectum , but none of the lymph nodes had tumor present and the resection margins were negative ( fig .
the patient is now undergoing adjuvant radiotherapy and there have been no other complications or signs of recurrence after 3 months of follow - up .
a 29-year - old man was referred from another urologic clinic for severe perineal pain with a weak urine stream and dysuria .
when he visited kyungpook national university medical center , he reported a history of acute urinary retention and had a foley catheter in place for about 1 month .
a digital rectal examination ( dre ) showed a relatively enlarged prostate with tenderness on pressure .
an abdominal computed tomography ( ct ) scan revealed an 874.5-cm - sized moderately enlarged prostate .
the estimated volume of the prostate by transrectal ultrasound ( trus ) and the prostate - specific antigen ( psa ) level were 80 ml and 8.0 ng / ml , respectively .
considering the relatively young age of the patient , acute bacterial prostatitis was suspected , but the patient 's clinical symptoms did not exactly line up with acute bacterial prostatitis . to relieve the patient 's symptoms and drain the urine
, we performed a suprapubic cystostomy and started the patient on intravenous antibiotics , but his symptoms were not relieved .
repeated trus and dre suggested a prostate cold abscess , but prostate malignancy could not be ruled out .
the prostate mri showed a huge prostatic mass that obstructed the bladder neck ( fig .
1 ) . according to the results of the mri , we performed transurethral resection of the prostate ( turp ) to relieve the bladder outlet obstruction and to confirm the pathologic nature of the mass . the pathology report from turp indicated high - grade sarcoma with extensive necrosis .
we performed chest ct and a whole - body bone scan to evaluate the extensiveness of the disease to determine the feasibility of surgery .
no metastatic lesions were found on the chest ct or whole - body bone scan . in the prostate mri , the whole prostate was shown to be involved by the malignant lesion and rectal wall invasion was suspected .
considering the particularly young age of the patient and the lack of evidence of bladder invasion , we decided to perform ralp and extended pelvic lymph node dissection , with an expectation of sparing the bladder .
this decision was made with the informed consent of the patient and the patient 's legal guardian . during the operation , rectal wall invasion of sarcoma was noted .
gross examination of the radical prostatectomy specimen showed a 128.07.0-cm - sized relatively well - demarcated mass containing hemorrhage .
the rectal mucosa and prostatic resection margins were positive for tumor , but none of the lymph nodes had tumor present ( fig .
the patient 's symptoms and the recurred mass in the pelvis became aggravated at 45 days after the operation .
a 45-year - old man was referred from another urology clinic for voiding difficulty lasting about 2 months . he had a history of gross hematuria and hematospermia lasting for 7 months until the present .
an abdominal ct scan revealed a 10126.4-cm - sized huge solid mass with focal cystic change in the pelvic cavity that was displacing the right ureter and with periprostatic fat infiltration and probable invasion into the urinary bladder , seminal vesicle , and rectum ( fig .
his estimated volume of the prostate by trus and his psa level were 575 ml and 1.19 ng / ml , respectively .
trus - guided prostate biopsy was performed to determine the nature of the tumor , which was revealed as a malignant spindle cell tumor with rhabdoid features , most likely pss .
we performed chest ct and a bone scan to determine the stage of the tumor and whether it had metastasized to other organs .
the chest ct and bone scan revealed no metastasis . considering the patient 's age and the aggressiveness of the disease
, open radical cysto - prostatectomy with an ileal conduit was performed . during the operation , rectal wall invasion of the sarcoma
gross examination of the radical cysto - prostatectomy specimen showed a 108.56.0-cm - sized prostate containing a bright yellow friable soft mass with central necrosis and a 9.06.05.0-cm - sized bladder with grossly noted pss invasion .
the final histopathologic analysis revealed pss with invasion to both seminal vesicles and the subserosal layer of the rectum , but none of the lymph nodes had tumor present and the resection margins were negative ( fig .
the patient is now undergoing adjuvant radiotherapy and there have been no other complications or signs of recurrence after 3 months of follow - up .
primary prostate sarcomas are rare tumors that account for less than 0.1% of primary prostate malignancy in adults .
pss is an even rarer form of sarcomas and the published cases number less than 30 .
generally , a prostate stromal lesion is classified into two categories : pspump and pss .
this division was made by gaudin et al .   in 1998 and by herawi and epstein   in 2006 on the basis of the degree of cellularity , mitotic figures , necrosis , and stromal overgrowth .
local recurrence and distant metastasis are quite common in pss ; however , the natural history of pspump is not well known .
reported that pspump is a benign disease entity and that in their series no patients developed evidence of sarcomatous transformation or malignancy .
the median survival time is less than 15 months , and only 10% of patients survive for more than 3 years .
reported that the overall 5-year actuarial survival rate for adult patients with prostate sarcoma was 38% . in our cases , the patient who was treated with ralp experienced recurrence of the tumor at 30 days after the surgery and was discharged for hospice care
the recurrence was aggressive in a short period with massive tumor formation in the pelvic cavity at 45 days after the operation .
few prostate malignancies except conventional adenocarcinoma have been treated with ralp owing to the aggressiveness and poor prognosis of such malignancies . especially in the case of pss , the low prevalence of the disease , the highly advanced state at the time of diagnosis , and the low survival rate are among the reasons why few surgeons make ralp their first choice . in our first described case , however , after considering several aspects such as the difficulty of anastomosis after wide excision , functional issues like continence and sexual potency , the relatively young age of the patient , the lack of evidence of bladder invasion , and the strong wishes of the guardian of the patient , we decided to perform ralp .
we experienced some difficulties resulting from the large prostate size and adhesions ; however , en bloc resection of the tumor was feasible .
the tumor in the second case was larger than the tumor in the first case and ct revealed invasion to multiple other adjacent organs , especially the bladder .
thus , considering the extent of the tumor , open radical cysto - prostatectomy with an ileal conduit was performed with adjuvant radiotherapy .
early diagnosis and complete surgical resection are the only means by which to expect a cure .
our recent experiences suggest that , in the case of pss , surgeons should approach the disease from the viewpoint of extensive surgical resection of the cancer rather than considerations of quality of life for the best chance of cure .
stromal sarcoma of the prostate is very rare and shows rapid growth , which consequently is related to poor prognosis . 
 recently , we treated two cases of prostatic stromal sarcoma : one with robot - assisted laparoscopic radical prostatectomy and the other with open radical cysto - prostatectomy with an ileal conduit . to the best of our knowledge , 
 this is the first case report of a prostatic stromal sarcoma managed by use of a robotic procedure . here , 
 we report of our experiences in the treatment of prostatic stromal sarcoma by use of two different methods .