A 46-year-old male presented in 2002 to an outside institution with five to six years of right hip pain radiating down the lateral thigh. Initial imaging is unavailable but by report radiographs showed a large mass involving the ischial tuberosity and portions of the adjacent inferior and superior rami of the right pelvis. He subsequently transferred care to our institution. Biopsies performed at the outside institution were reviewed and confirmed giant cell tumor of bone. He subsequently underwent partial internal hemipelvectomy in November 2002. Histopathologic analysis showed GCT (Figure 1).
Postoperatively, the patient was started on alendronate (dose unknown). Follow-up MRI in February 2003 showed an enhancing, high T2 signal, 2 cm soft tissue mass within the right adductor musculature, adjacent to the former location of the ischial tuberosity, suspicious of recurrence. CT imaging in August 2003 showed a mass within the surgical bed, within the obturator externus and pectineus muscles, and abutting the root of the penis. CT guided biopsy confirmed recurrent benign GCT. Reexcision of the mass was performed in September 2003. The pathology specimen showed a 4 cm mass embedded within excised soft tissue. Giant cell tumor was present at multiple resection margins.
Postoperatively, the patient did well, with intermittent complaints of pain. Follow-up MRI eight months after surgery showed an enhancing multilobulated mass at the margins of the original hemipelvectomy surgical bed, the largest mass measuring up to 2.7 cm. Edema and abnormal enhancement were noted within the obturator externus, obturator internus, and quadratus femoris muscles. Another 1.5 cm nodule was noted in the proximal adductor brevis muscle. He was subsequently followed up with approximately yearly MRI studies. The recurrent tumor showed progressive, interval growth, reaching a measurement of 3.2 x 3.6 cm in December 2005 (Figure 2), 9.2 x 3.4 cm in January 2008, and 11.0 x 8.9 cm in January 2012, at which time there was possible invasion into the right corpus cavernosum.
The patient was started on denosumab (120 mg subcutaneous monthly) in July 2012. Imaging over the next 2 years showed stable disease, with possible slight decrease in size of the tumor. In November 2014, the patient developed osteonecrosis of the left mandible after tooth extraction, and denosumab was held for two doses. Denosumab was restarted in late December 2014 after presenting to clinic with severe right groin pain radiating inferiorly. Follow-up CT scan in February 2015 showed enlargement of the pelvic mass to 13.6 x 13.0 cm with extension into the ischioanal fossa and subsequent mass effect on the rectum, prostate, bladder base, and base of penis (Figures 3 and 4). The imaging findings were highly suggestive of sarcomatous transformation of the GCT. Multiple nodules were also now noted throughout the lungs. No additional potential primary tumor that could account for the lung nodules was identified on imaging, and metastases from a malignant GCT were suspected. Denosumab was discontinued.
CT guided biopsy of a right lower lobe nodule showed a high grade spindle cell sarcoma with nuclear atypia and low mitotic rate (up to 4 mitoses per high power field) (Figure 5). By immunohistochemistry, the tumor stained for smooth muscle actin (SMA) and p63, with focal S-100 protein staining. Subsequent CT guided biopsy of the pelvic mass revealed a high grade sarcoma with discohesive round to epithelioid cells that expressed SATB2 and weak SMA and lacked p63 (Figure 6). The morphology and IHC staining results were consistent with transformation to osteosarcoma.
Subsequent CT scan showed interval increase in size of the pelvic mass, an increase in the number and size of lung nodules, pulmonary lymphadenopathy, and a hepatic lesion suspicious of additional metastasis. The patient was started on doxorubicin and ifosfamide. CT scan showed slightly decreased primary tumor but an increased number of pulmonary nodules, two liver lesions, inguinal lymphadenopathy, and a probable 3.7 cm metastasis to the penis. He was then started on docetaxel and gemcitabine. He transferred care from our institution shortly thereafter.