Primary Bladder Osteosarcoma: A Rare Entity with an Unfavorable Prognosis

Primary extraosseous osteosarcomas are a rare occurrence that can affect the kidneys, brain, lungs, heart, and breasts.^3,4 In order to diagnose primary extraosseous osteosarcoma three factors must be met: a consistent morphological structure of sarcomatous tissue is evident and rules out a mixed malignant mesenchymal tumor, the production of malignant osteoid by sarcomatoid tissue, and the elimination of the possibility of an osseous source.^3,4

Primary urinary bladder osteosarcoma is an extremely rare variant of osteosarcoma, having less than 40 recorded cases and accounting for <0.05% of urinary bladder cancers.² This malignancy has been noted primarily in males; however, due to limited data, the ratio for male-to-female prevalence has been reported to be anywhere from 2:1 - 4:1.^2,7 Analysis of recorded cases showed a reported age range anywhere from 24-83 years old at the time of diagnosis.^5-14 Upon presentation, patients had a wide array of symptoms, but common symptoms seen amongst the cases included: dysuria, hematuria, and flank pain.^2,7-10 Additionally, a majority of individuals diagnosed with primary urinary bladder osteosarcoma were noted to have comorbidities; however, cyclophosphamide usage and a previous history of transitional cell carcinoma were comorbidities that have raised suspicion of increasing susceptibility to primary urinary bladder osteosarcoma.^9,11

Currently, treatment of primary urinary bladder osteosarcoma varies based on patients’ age, comorbidities, personal preferences, and extent of the cancer. Most cases have been treated with segmental or complete cystectomy with pelvic/abdominal lymphadenectomy and resection of surrounding affected structures – sometimes with adjunctive chemotherapy and radiation.^2,6-11

Differential diagnosis of primary urinary bladder osteosarcoma includes stromal osseous metaplasia of urothelial metastasis, carcinosarcoma of the bladder, and urothelial cell carcinoma of the urinary bladder.^15-18 The listed malignancies have similar clinical presentations consisting of hematuria, dysuria, issues with voiding, and abdominal/pelvic pain. Additionally, computed tomography imaging of the cancers are quite similar as well showing pelvic masses with heterogeneous areas of necrosis and hypoattenuation.^16-18 However, upon histological analysis, primary urinary bladder osteosarcoma yields a unique pattern of spindle shaped cell bundles within a lace-like osteoid matrix.^2,7-8 Stromal osseous metaplasia of urothelial metastasis and urothelial cell carcinoma of the urinary bladder show matured osseous metaplasia, while carcinosarcoma of the bladder shows sarcomatoid and epithelial features.^16,17

Given the rarity of primary osteosarcoma of the urinary bladder, this case lends itself to further adding to the information collected from the past case studies. According to Oka et al., there have been a total of 38 reported cases of primary bladder osteosarcoma, making this study the 39th case according to the analyzed data.¹ The patient in this case fell within the age range at time of diagnosis when compared to the previous studies, and had similar microscopy to previous studies. Also, this individual’s symptoms were aligned with most previous cases – including flank pain and gross hematuria. Where this case differs from previous cases is both in the macroscopy of gene paneling. In comparison to previous cases, the presented case showed a much higher degree of local invasion by the cancer warranting a complete cystectomy of the bladder with ureteroileal conduit/sigmoid bladder pelvic lymphadenectomy along with robotic total abdominal hysterectomy and partial vaginectomy due to extraperitoneal bladder perforation as well as possible cecum-bladder fistula (Figure 2). Also, in comparison to previous research, extensive gene paneling was conducted on the pleomorphic sarcoma, which showed PIK3CA, FGFR3, TP53, KDM6A, STAG2, and TERT somatic mutation.