Abstract
Tumour-to-tumour metastasis is very unusual and has been defined as a tumour metastasis into another histologically different tumour. It is extremely rare in bone. We report a case of lung squamous cell carcinoma metastasized to an enchondroma in the femur of a patient with Ollier disease. A 60-year-old female had a history of a poorly differentiated squamous cell carcinoma of the lung. She underwent a video-assisted thoracoscopic lobectomy, and a follow-up MRI scan showed three lesions in the left distal femur and proximal tibia, which were initially interpreted as metastasis on radiology. Resection of the left proximal tibial lesion was performed, and the pathological findings were consistent with enchondroma with no evidence of metastasis. Subsequent curettage of lesions in the distal left femur revealed metastatic poorly differentiated carcinoma with foci of hyaline cartilage, which was most consistent with metastatic carcinoma in a pre-existing enchondroma. The MRI films were re-reviewed. Characteristic MRI features of enchondroma were found in the lesion in the left proximal tibia and one of the lesions in the left distal femur, while the features of the other lesion in the left distal femur included cortical destruction and extensive oedema in surrounding soft tissue, which were consistent with a malignant tumour. In addition, the enchondroma in the lateral condyle showed blurring and irregular inner margin and adjacent bone oedema, which likely represents a co-existing metastatic tumour and enchondroma. The difference in lineage was confirmed by immunohistochemistry. The final diagnosis was metastatic poorly differentiated carcinoma of the lung into a co-existent enchondroma. The diagnosis can be challenging and could be easily overlooked both radiologically and histologically. Thorough clinical and radiological information is critical for the diagnosis, and despite a very unusual event, awareness of the tumour-to-tumour metastasis phenomenon can avoid an inaccurate diagnosis by the pathologist, therefore preventing inappropriate clinical intervention.
Highlights
Tumour-to-tumour metastasis is a rare phenomenon that has been described as an occurrence of distant tumour metastasis into another histologically different tumour
Metastases are the most common type of malignancy involving the skeleton, and lung carcinoma is the second most common malignant tumour metastasizing to the bone both in women and men [3]
Berent first reported a case of metastatic squamous cell carcinoma from the jaw into renal cell carcinoma [6]
Summary
Tumour-to-tumour metastasis is a rare phenomenon that has been described as an occurrence of distant tumour metastasis into another histologically different tumour. We present a case of a patient with Ollier disease with multiple enchondroma [1] and within an enchondroma in the femur a tumour-to-tumour metastasis from a lung squamous cell carcinoma. This report is the first case of tumour-to-tumour metastasis from a lung carcinoma to an enchondroma in the context of Ollier disease. The differential diagnosis on morphology was dedifferentiated chondrosarcoma (ex enchondroma in Ollier disease) or a metastatic carcinoma towards a pre-existing enchondroma. It was consistent with metastatic squamous cell carcinoma, but the additional cartilaginous component was puzzling. The lesion located in the lateral condyle showed blurry and irregular inner margin and adjacent bone oedema, which should be the co-existing tumour metastasis and enchondroma. The patient expired approximately 1 year after the initial diagnosis
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