Atypical bone metastasis and radiation changes in a colon cancer: a case report and a review of the literature.

We report a unique case of skeletal metastasis with prominent soft tissue extension from a colon cancer in a 44-year-old male patient. Four years after the diagnosis of colon cancer, plain radiographic examinations revealed a prominent soft tissue mass associated with cortical destruction of the right femur. Palliative radiotherapy of the right femur was performed. After completing radiotherapy, massive remineralization was seen in the soft tissue component. With the assistance of pre- and post-radiotherapy computerized tomography images, obtained in the process of planning the radiotherapy, we reached the conclusion that in our case the pre-radiotherapy finding was an extreme case of eccentric expansion of the bony cortex due to the outgrowth of bony metastasis. Retrospectively, the initial prominent soft tissue mass associated with the cortical destruction seems to have been a protruding bone metastasis, extending from the medial aspect of the right femur. This peculiar feature with remineralization after radiotherapy should help explain the phenomenon of atypical bony metastasis from a radiological perspective.