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:
a 40year old female non  smoker of average build , presented with swelling in the left lumbar region along with dragging pain for 3 months , with no history of dysuria , hematuria , trauma or previous surgery .
she was non  hypertensive and non  diabetic and had no family history of malignancy .
ultrasonography ( usg ) showed a large ( 17.4  13  12 cm ) predominantly cystic mass with solid components and internal septas which appeared to be arising exophytically from the lower pole of the left kidney .
on further evaluation , the ct findings showed a large ( 19  14  17 cm ) left retroperitoneal mass with solid and cystic components on the inferior aspect of the left kidney ( figure 1 ) showing effaced fat planes , inseparable from the lower pole of the kidney , with mild  moderate left hydronephrosis due to compression of the left ureter .
soft tissue stranding was observed in the adjacent retroperitoneal fat and thickening of the perinephric fat .
her liver and renal function tests , along with chest x  ray , did not reveal any abnormalities .
ct image showing a 19  14  17 cm left retroperitoneal mass with solid and cystic components in the left kidney .
the patient underwent a left nephrectomy . a tan to grey coloured growth , measuring 16  15 cm , with fleshy consistency and golden yellow discoloration , along with areas of necrosis and haemorrhage ,
chromophobe rcc , as the carcinomatous element , is comprised of groups of polygonal cells with resinoid nuclei , perinuclear halo and prominent cell membranes ( figure 2 ) .
the sarcomatoid component is represented by pleomorphic spindle cells in between forming fascicles at places , fibrosarcoma  like pattern , occasionally tumour gaint cell and bizarre forms noted , furhman nuclear grade was 3 , comprising 4050% component in tumour ( figure 3 ) .
the tumour was unifocal , limited to the lower pole , raising the capsule , but not infiltrating it .
the morphology and ihc study were suggestive of the chromophobe type of rcc with sarcomatoid differentiation .
ct of the thorax was done to search for metastasis , but did not reveal any abnormal findings . considering the aggressive nature of the tumour ,
the patient was advised to have adjuvant chemotherapy . due to the patient 's reluctance for chemotherapy
, she was given the option to remain under close observation with usg / ct scan .
the patient is disease free after one year of treatment and is still under observation . 
 
hematoxylin  eosin stained section ( a : chromophobe renal cell carcinoma cell nests with fascicles of spindle cells in between ) .
the cells had eosinophilic cytoplasm with accentuated cell borders and centrally located nuclei that had wrinkled peripheral borders and varying degrees of hyperchromatism ( magnification 10 ) .
the spindle cells were arranged in ill  defined fascicles that had a focal storiform pattern , mitoses and some bizarre forms .
ihc studies showing epithelial cells positive for pan  cytokeratin and ema , whereas spindle cells are negative for ema and few are positive for pan  cytokeratin .
ihc studies showing spindle cells positive for cd10 and vimentin , whereas epithelial cells are negative .
chromophobe rcc is the third most common histologic subtype , accounting for less than 5% of rccs .
renal vein invasion is seen in less than 5% of cases . despite the overall favourable prognosis
sarcomatoid rcc of the kidney , constituting about 15% of all renal malignant neoplasms , are clinically aggressive tumours with rapid spread and poor overall survival . in a study done by de peralta 
venturina et al , the incidence of sarcomatoid changes in rcc was found to be 10.6% in 952 cases studied .
the incidence of sarcomatoid changes was highest ( 29% ) in collecting duct carcinoma ( 2 of 7 cases ) , followed by 11% ( 3 of 27 cases ) in unclassified rcc , 9% ( 5 of 53 cases ) in chromophobe rcc and 8% ( 59 of 720 ) in clear cell rcc .
this process is thought to result from dedifferentiation of the epithelial component , and so the sarcomatoid cells are expected to show the original genomic pattern of the  parent  cells .
the sarcomatoid dedifferentiation in any type of rcc carries a poor prognosis for most patients , and most of them present with an advanced stage at initial diagnosis .
specific survival rate was found to be 22% and 13% after 5 and 10 years respectively , as compared with rcc without sarcomatoid changes with a 5 and 10 year disease 
the amount of sarcomatoid component ( equal to or more than 50% ) and lymphovascular invasion are associated with decreased survival .
patients are 3 times more likely to die of rcc if they have distant metastasis or tumor necrosis at the time of radical nephrectomy .
the presence of a sarcomatoid component was significantly associated with poor outcome even after adjusting for tnm stage , tumour size , and histologic tumour necrosis .
detection of sarcomatoid rcc has an important prognostic significance , as reflected by its aggressive behaviour , propensity to metastasize and association with the overall poor survival .
fortunately , the case reported here presented at an early stage , when the disease was localised within the renal capsule , with no detectable metastasis .
we have reviewed our case with one of the largest series of chromophobe rcc with sarcomatoid changes , where lauer et al . found male predominance ( 64% ) with 60.4 years as the mean age of presentation .
akhtar et al . had a female predominance ( 66% ) with 57 years as the mean age of presentation [ 6 , 7 ] .
our patient is a 40 year female , who is comparatively young as compared to the case series data .
sided disease in the series by lauer et al . , whereas akhtar et al . found an equivalent number on both sides [ 6 , 7 ] .
the tumour size ranged from 9.528.0 cm in the study done by lauer et al . and the mean size reported by akhtar et al .
was found to be 11 cm [ 6 , 7 ] . in both series , all patients had local spread of the disease and 2030% had metastasis during the time of presentation [ 6 , 7 ] .
our patient had a left sided tumour , 19 cm in size , but there was no local spread or distant metastasis at presentation . compared with classic chromophobe rcc , an analysis of 61 cases by peryomaure et al .
found that the most common pathologic stage tumour was t1 in 65.6% of cases , and t2 in 31.1% patients .
it is suggested that sarcomatoid chromophobe rcc is a more aggressive neoplasm compared with classic chromophobe carcinoma .
they demonstrated a very poor prognosis in the sarcomatoid chromophobe cell carcinoma compared with classic chromophobe cell carcinoma .
our case represents a sarcomatoid chromophobe cell carcinoma with no local spread and no metastasis .
this unusual renal cancer has the potential to behave aggressively and to metastasize , but , in our case , the patient was under close observation with no adjuvant treatment , and there is no evidence of disease one year after the surgery .
our case gives an option of close observation instead of chemotherapy in cases where there is no disease outside the renal capsule , despite having a sarcomatoid differentiation in chromophobe renal cell carcinoma .
chromophobe renal cell carcinoma ( rcc ) , a subtype of rcc , accounts for 46% of all rcc and has better prognosis then conventional rcc . 
 sarcomatoid dedifferentiation is thought to represent the high  grade end of all subtypes . 
 this makes chromophobe rcc with sarcomatoid changes a rare entity associated with poor prognosis in most studies . 
 we present a case of a 40year old female with this rare histology , with the tumour localised to the renal capsule , managed with nephrectomy and with close follow  up thereafter . 
 the patient is free of disease after one year of treatment .