Besides conventional chondrosarcoma, several rare chondrosarcoma subtypes are described, comprising about 15% of all chondrosarcomas. Clear cell chondrosarcoma (CCS) is a low-grade malignant tumour, often recurring after curettage, and showing overall survival of about 85%. Mesenchymal chondrosarcoma (MCS) is a highly malignant tumour occurring in bone and soft tissue of relatively young patients. The tumour shows differentiated cartilage mixed with undifferentiated small round cells. It often metastasises and shows a 5-year overall survival of 55%. Dedifferentiated chondrosarcoma (DDCS) is a tumour containing a high-grade non-cartilaginous sarcoma (DD), and a usually low-grade malignant cartilage-forming tumour (WD).

The prognosis is poor. The lack of efficacious treatment of these rare tumours emphasises the need to learn more about their characteristics and to unravel potential targets for therapy.

We constructed tissue microarrays (TMAs) with 2mm cores of 45 DDCS (WD and DD), 24 CCS, and 25 MCS, in triplicate.

Using immunohistochemistry, we investigated protein expression of estrogen-signaling molecules, growth plate-signaling molecules, and other molecules which might be potential targets for therapy. In addition, we gathered genomic information using Agilent 44K oligo arrays.

30% of the WD components were positive for Cox-2. Almost all others were negative. For Bcl2, 88% of the small cells and 32% of the cartilage in MCS were positive. In CCS, WD, and DD 48%, 4%, and 12% were positive, respectively. We demonstrated the presence of ESR1 and aromatase protein in the majority of tumours in all subtypes. Using array CGH, we observed similar aberrations in the two components of DDCS, with additional aberrations in the DD.

Celecoxib treatment is not recommended, as most of the tumours are negative for Cox-2. However, the presence of ESR1 and aromatase support a possible effect of anti-estrogen treatment in all subtypes, and application of Bcl2 inhibitors might chemosensitise MCS.

Multifocal osteolytic lesions of the skeletal system are a challenge regarding diagnosis especially when multi-nucleated giant cells which are not specific for a tumour entity are found in the histological specimen. Therefore multiple differential diagnosis have to be considered such as metastases, primary malignant bone tumours, multicentric giant cell tumour of bone and brown tumours of primary hyperparathyroidism.

A 49 year old woman underwent medical investigation in an external surgical department due to right hip pain after a fall. The radiologic skeletal status surprised with multiple osteolytic pelvic lesions and one tumour in the left scapula and first histological diagnosis described a giant cell tumour of bone with malignant aspects. After confirmation of this diagnosis by a second histopathological inquiry accomplished by a bone tumor specialist the patient was transferred to our tumour centre. To exclude the differential diagnosis of brown tumours a close look on the parathormon level was done which revealed an exorbitantly high serum amount of 922.7 pg/ml (normal 15–65 pg/ml). Further examination confirmed a parathyroid adenoma. After its extirpation serum levels of parathormon decreased and two months after therapy with high dose calcium substitution radiologic controls show a decline of osteolysis with bone consolidation.

Brown tumours of hyperparathyroidism have always to be considered as a rare differential diagnosis of multiple giant cell containing tumours. The disease cannot be distinguished by the histological pattern but can very easily be excluded by normal parathormon levels. First step of therapy in brown tumours should be surgical extirpation of parathyroid adenomas or carcinomas followed by an endocrinological regime. Only failure of this treatment requires further surgical stabilisation of the bone lesions.

Periprosthetic osteolysis after total joint replacement is a well described complication. This normal slowly increasing process is caused by infection, implant loosening or more special, debris induced. However malignant processes may rarely occur at exact this location too. Based on clinical presentation and imaging it is sometimes difficult to exclude a local malignant process. We report two cases of extensive osteolysis after total hip replacement, including their follow up and a review of the relevant literature.

Two female patients developed massive osteolysis in periprosthetic areas (pelvic area and proximal femur as well as distal femur) after being treated by total hip arthroplasty 14 and 18 years ago. In both cases a tumorous process was suspected after imaging and they were therefore referred to our clinic. In one case a rapidly progressing soft tissue swelling with extensive peri-articular osteolysis was considered to be a malignant tumour. After an incisional biopsy, an embolisation had to be performed due to continuous massive bleeding. Histology revealed a superinfected polyethylene disease, treated with a two stage revision surgery. The second patient presented with an impending fracture due an unusual osteolysis at the tip of the stem. Here again polyethylene debris was found at biopsy.

Extensive osteolysis and/or soft tissue swelling caused by polyethylene debris may sometimes be difficult to differ from a tumorous process. As a guideline presented by Min WK. et al in 2008 a reactive bone-destroying process normally proceeds slowly in contrast to a more rapid progression in malignant disease. However, as presented in the first of our cases, exemptions may occur. In these cases a biopsy or at least a frozen section at operation should be obtained in order to exclude a real neoplasm.