Tumor weight following induction of subcutaneous tumors with SRC cells overexpressing either thymosin-β4 or c-fos. Control tumors were initiated with SRC cells that express the MSCV viral vector with no insert (pMSCV-I-Hygro vector). C-fos tumors were initiated with SRC cells that overexpress c-fos (MSCV-cfos-I-Puro). Thymosin-β4 tumors were initiated with SRC cells that overexpress thymosin-β4 (MSCV-Thyβ4-I-Puro). Overexpression of c-fos resulted in the formation of tumors that were significantly smaller than control tumors. The bar represents the average invasion indices of biologic replicates, and the error bars represent the standard deviation of the biologic replicates. '*' Indicates that the tumor weight is significantly different than the tumor weight of the control tumors (p-value <0.05 considered significant). n = 10 for control tumors and c-fos tumors. n = 9 for thymosin-β4 tumors (one animal died prematurely and was found to have multiple chondrosarcoma lung metastases). See Additional file 4 for complete list of tumor weights. (B) Photomicroscopy of histological sections obtained from SRC tumors (20 × magnification). Tumors induced from control cells (SRC cells expressing the empty viral vector), and from SRC cells overexpressing either Thymosin-β4 (Thymosin-β4 tumor) or c-fos (C-fos tumor). Approximately 30 days following tumor induction animals were sacrificed and tumors were removed for histology. Sections representative of each tumor are shown. All tumors were classified as histologic grade II chondrosarcomas. The SRC cells are stained with Safranin O (red).