a renal leiomyosarcoma is an uncommon neoplasm of the kidney , accounting for approximately 1% of all malignant renal tumors , and has a poor prognosis [ 1 , 2 ] . its symptoms , such as nonspecific abdominal discomfort , dull pain , and oliguria , are common in other conditions ; therefore , a renal leiomyosarcoma is difficult to diagnose preoperatively . in this case , the condition had been preoperatively misdiagnosed four years earlier as a renal cell carcinoma before it was diagnosed as a primary renal leiomyosarcoma . furthermore , it took several months to diagnose a recurrent renal leiomyosarcoma in the same patient because of the ambiguous , nonspecific symptoms . she visited our clinic complaining of diffuse abdominal pain , and colonoscopy showed a submucosal tumor or an extrinsic mass involving the descending colon . there are no reported cases of a renal leiomyosarcoma invading the retroperitoneal colon and mimicking a submucosal lesion . a 57-year - old woman visited our gastroenterology department complaining of diffuse lower abdominal discomfort . the preoperative diagnosis was a renal cell carcinoma , but she was subsequently diagnosed with a primary renal leiomyosarcoma on pathologic examination ( fig . regular follow - ups with a urologist and abdominal computed tomography ( ct ) showed no recurrence for three years . after another year , she returned to the hospital complaining of diffuse abdominal discomfort . at that time the findings of a general physical examination were unremarkable , except for diffuse abdominal sensitivity . the laboratory test results were as follows : leukocyte count , 6,770/mm ; hemoglobin level , 12.0 g / dl ; and platelet count , 276,000/mm . the levels of aspartate aminotransferase ( 12 iu / l ) , alanine transaminase ( 10 iu / l ) , alkaline phosphatase ( 82 iu / l ) , and total bilirubin ( 1.2 mg / dl ) were within the reference range . colonoscopy revealed a hemispheric lesion similar to a submucosal tumor in the descending colon , approximately 30 cm above the anal verge ( fig . the larger lesion was located in the peritoneum , adjacent to the anterior portion of the descending colon , and the smaller lesion was located in the retroperitoneum , adjacent to the posterior portion of the descending colon . pet - ct showed a large omental mass on the left side of the abdomen , with a small solid area of increased glucose metabolism and hypermetabolism ( maximum standardized uptake value of 13.7 ) , in the posteromedial portion of the mid - descending colon ( fig . 4 ) . a laparoscopic tumorectomy and segmental resection of the descending colon were performed . examination of the gross specimen revealed a firm white mass approximately 10  9 cm and a 2  2 cm mass invading the descending colon ( fig . the number of mitoses was between 10 and 19 in each of 10 high - power fields ; hence , the histologic grade was high . the microscopic examination (  20 magnification ) of a section stained with hematoxylin and eosin revealed a solid tumor mass , well demarcated by a capsule with a peripheral zone . fascicles of spindle cells with elongated and blunt - ended nuclei were visible at  100 magnification ( fig . the patient then received two cycles of mesna , adriamycin , ifosfamide , and dacarbazine ( maid ) chemotherapy at the oncology department . leiomyosarcomas are cancers of the smooth muscle cells , which can arise at any location . the uterus , the retroperitoneum , and the intra - abdominal cavity are common primary sites . this tumor is most commonly seen in the fifth and the sixth decades of life , and the male - to - female ratio is 1:2 . high - grade leiomyosarcomas frequently metastasize , and the most commonly affected organ is the lung . prognosis is poor , and the five - year survival rate is 29 - 36% . in most reported cases , presentations are nonspecific and the results of physical examinations are normal . radiologic features are nonspecific ; therefore , it is difficult to diagnose this cancer preoperatively . four years earlier , our patient had also been diagnosed preoperatively as having a renal cell carcinoma based on radiologic examination , the physical examination findings having been nonspecific . leiomyosarcomas are distinguished from leiomyomas by cellular pleomorphism , an increased mitotic rate , and the presence of cellular necrosis . furthermore , in this case , our pathologist conducted immunohistochemical staining , which is useful in the diagnosis of leiomyosarcoma . immunohistochemical staining revealed positive findings for vimentin and smooth muscle actin and desmin . if a leiomyosarcoma specimen is found to have a pleomorphic component on immunohistochemical staining , it is difficult to distinguish it from a malignant fibrous histiocytoma . however , such heterologous differentiation was not observed in this case [ 6 , 7 ] . a good prognosis can be expected only with complete surgical excision ( the treatment of choice ) [ 8 - 10 ] . irradiation therapy and chemotherapy do not alter the course of the disease and are not successful in metastatic lesions . a tumor size of less than 5 cm , low histological grade , absence of lymph node metastasis , and radical excision of the mass are all associated with an improved prognosis . to have ensured a better prognosis in this particular case , a radical nephrectomy should have been performed as the first operation . unfortunately , as the patient had been thought to have a renal cell carcinoma in the preoperative state , she instead underwent a simple left nephrectomy . a submucosal tumor is defined as an elevated or polypoid mass covered with normal mucosa . several colorectal diseases , such as lipoma , leiomyosarcoma , lymphangioma , and carcinoid tumor , can be detected as lesions mimicking submucosal tumors . we also confirmed the lesion in the descending colon as being caused by extrinsic compression by performing a ct scan . as observed in this case , recurrence of a leiomyosarcoma in the retroperitoneum needs to be considered in the differential diagnosis of submucosal tumors in the colon . thus , we report this unusual , but interesting , case of recurrence of a rare renal leiomyosarcoma .
a primary leiomyosarcoma of the kidney is a rare , but highly aggressive , neoplasm , accounting for only 0.1% of all invasive renal tumors . 
 local or systemic recurrence is common , but a leiomyosarcoma is difficult to diagnose preoperatively . 
 we recently encountered an interesting case of an unusual recurrence of a renal leiomyosarcoma . 
 a 57-year - old woman visited our hospital complaining of lower abdominal pain . 
 four years previously , she had undergone a left nephrectomy . 
 she had a primary leiomyosarcoma of the kidney that had been misdiagnosed as a renal cell carcinoma . 
 colonoscopy revealed the presence of a lesion similar to a submucosal tumor in the descending colon . 
 postoperative pathologic examination confirmed that the mass was a recurrent leiomyosarcoma . 
 we report this unusual case and present a review of the literature .