A 43-year-old Malay man presented to our facility with a three-month history of fever, non-productive cough and weight loss. He was a chronic smoker and had no significant medical history. Results of a physical examination were unremarkable. A chest radiograph revealed a large right lower zone lung lesion, and a subsequent computed tomography (CT) scan of the thorax and abdomen revealed a large heterogeneously enhancing soft tissue mass in the right lower lobe of the lung with intra-cavitary extension into the left atrium via the right inferior pulmonary vein (Figure ). Transthoracic needle aspiration of this mass was suggestive of carcinoma. Surgery was performed for the resection of this mass; a right posterior lateral thoracotomy was performed, followed by a right lower lobectomy. The left atrium was opened at the inferior part of the superior pulmonary vein and the tumor resected with a small cuff of left atrium. The entire tumor and right lower lobe was delivered en bloc, and the left atrial defect subsequently patched. Histology demonstrated a high-grade clear cell sarcomatoid tumor, suggestive of metastatic clear cell renal cell carcinoma, a diagnosis specifically considered by the pathologist. On immunohistochemistry, the lesion was focally positive for epithelial membrane antigen (EMA), CD10 and vimentin, but negative for anticytokeratin CAM5.2, thyroid transcription factor-1 (TTF-1), smooth muscle actin (SMA), S100, HMB-45, Melan-A, Hepar and synaptophysin. However, as no renal lesion was evident on the CT scan (Figure ), a diagnosis of alveolar soft part sarcoma was considered. An additional extensive investigation did not reveal a primary lesion or any other metastatic lesions.\nThen, four months later, our patient developed a subcutaneous mass in his left loin. A CT scan of the abdomen confirmed a large 11 cm tumor occupying nearly the entire right kidney with involvement of the pelvicalyceal system and proximal ureter (Figure ). The tumor also extended into the right renal vein and the inferior vena cava, with a 2 cm soft tissue nodule was seen in the subcutaneous layer of the left flank. Further imaging of the thorax demonstrated multiple lung nodules, a large right pleural-based mass and an enlarged subcarinal lymph node. A bone scan was performed, and suggested involvement of the right humeral head and multiple thoracic vertebrae. Excision biopsy of the subcutaneous nodule was performed, and histology demonstrated a tumor morphologically similar to the initially resected lung lesion, suggestive of a high-grade clear cell renal cell carcinoma with sarcomatoid differentiation (Figure ). On immunohistochemistry, the tumor was strongly positive for vimentin, CD10, focally positive for epithelial membrane antigen, melan-A and negative for TTF-1, S100, inhibin and synaptophysin (Figure ) The positive vimentin and negative inhibin results weighed against the likelihood of an adrenocortical tumor.\nOur patient was given palliative first-line therapy of sunitinib, with initial best response of stable disease. After three cycles of sunitinib, the disease progressed; our patient declined any further therapy and he eventually died 13 months after his initial lung resection.
A 49-year-old male was presented at our department with lower back pain and walking instability for the last few days. The patient suffered from end-stage renal disease on dialysis for the last 15 years and had a history of successful renal transplantation about 25 years ago. The initial renal insufficiency resulted from a chronic glomerulonephritis and the allograft was rejected 9 years after transplantation due to the same underlying condition. Furthermore, about 2 years ago, he underwent bilateral nephrectomy for solid tumorous masses in both nonfunctioning kidneys. The histologic examination revealed, bilaterally at that time, type 1 papillary renal cell carcinoma (pT1aN0M0, Fuhrman grade II, in sano resection). Additionally, the nonfunctioning transplant kidney was removed about 6 months ago due to recurrent episodes of macrohaematuria, without evidence for a malign tumour. At that time, there were no signs for a metastatic disease.\nAt current presentation, the performed magnetic resonance imaging (MRI) of the spine showed a pathologic facture at the right side of the first and second lumbar vertebral body () from a metastatic solid mass, as well as multiple osteolytic metastases from 7th cervical to 2nd lumbar vertebra. A staging computed tomography (CT) of the thorax and abdomen showed further osseous osteolytic metastatic lesions at the sternum, both scapulae, the bone pelvis, and the left proximal femoral bone. The performed biopsy of the osteolytic metastatic lesion at the second lumbar vertebra revealed a metastatic, mucin-poor variant, of a mucinous tubular and spindle cell carcinoma of the kidney (). A thorough reexamination of the old nephrectomy specimens showed that the tumour of the right kidney was also a mucin-poor variant of a MTSCC of the kidney, while the tumour of the left kidney was confirmed as a papillary RCC.\nHistologically, both the biopsy sample and the nephrectomy-specimen of the right kidney showed a renal cell tumour with a spindle cell component, as well as tubular and papillary parts without any clear cells. Both spindle and tubular-papillary parts were delimited by a basal membrane, forming a ball-shaped, epithelial tumour-growth pattern with spindled nuclear morphology, which did not match a sarcomatoid differentiation. Immunohistochemically, the tumour was negative for desmin and actin and S100 protein, as well as for HMB45, MITF1, MART1, and SOX-10. A positive reaction to Racemase (AMARC), PAX-8, and RCC was found, with focal positivity for CD10. Pan-Cytokeratin (AE1/AE3) and CK7 were negative except from the papillary parts. The Ki67 stain showed focal proliferation rates up to 30%. Furthermore, no mucoid interstitial matrix was found with H&E stain. Only with Alcian blue staining, <1% mucin in cellular areas was observed.\nAccording to our interdisciplinary tumour conference board's recommendation, the patient followed a systemic treatment with pazopanib and focal radiotherapy to lumbar and cervical vertebrae metastases. In further follow-up, irrespective of the started treatment, the tumour spread rapidly and after three months the patient presented with additional hepatic and pulmonary metastases. The patient finally succumbed to the disease a few months later.