The sacrum is a large, triangular bone composed of five fused vertebrae, situated at the base of the spine and connecting it to the pelvis. This structure bears the entire weight of the upper body, supporting posture, balance, and mobility. A primary sacral tumor, cancer originating directly in this bone, is extremely rare. It presents a serious challenge due to the sacrum’s close proximity to major nerves and blood vessels. Life expectancy depends on the specific tumor type, the extent of the disease, and the success of multidisciplinary treatment.
Defining Primary Sacral Tumors
Sacral cancer refers to a small group of primary malignant tumors, each originating from different cell types and exhibiting distinct biological behaviors. Prognosis depends heavily on identifying the specific cell origin, which determines the tumor’s growth rate and responsiveness to therapy. The two most frequent primary malignancies found in the sacrum are chordoma and chondrosarcoma.
Chordoma is the most common primary sacral tumor, arising from remnants of the embryonic notochord, the precursor to the spinal column. It is characterized by slow, locally aggressive growth and a high tendency for local recurrence, even decades after initial treatment. These tumors test positive for the protein brachyury, which helps distinguish them from other sarcomas.
Chondrosarcoma, the second most common type, originates from cartilage-forming cells and typically grows more slowly than other high-grade sarcomas. Its behavior depends heavily on its grade, ranging from low-grade lesions that rarely metastasize to high-grade, aggressive types like dedifferentiated chondrosarcoma. Chondrosarcomas do not stain for brachyury, providing a clear distinction from chordoma. They generally have a better long-term prognosis than chordoma, except for the most aggressive variants.
Staging and Tumor Grading
Oncologists use a standardized system to accurately describe the extent of the cancer, which determines prognosis and guides treatment decisions. The American Joint Committee on Cancer (AJCC) TNM system is commonly applied to these sarcomas. This system incorporates information about the primary tumor (‘T’), lymph node involvement (‘N’), and metastasis (‘M’). Larger tumors (‘T’) are associated with a significantly increased risk of death.
The ‘M’ component indicates whether the cancer has spread to distant sites (metastasis), such as the lungs. Metastasis immediately classifies the disease as Stage IV and significantly worsens the outlook. Lymph node involvement (‘N’) is rare in most sacral sarcomas but is still assessed. The staging also incorporates the tumor’s grade (‘G’), which reflects how abnormal the cancer cells appear and their likely speed of multiplication.
Tumor grading is particularly significant for chondrosarcoma, which is typically graded from I (low-grade) to III (high-grade). Low-grade tumors (Grade I) grow slowly and are much less likely to spread. Conversely, high-grade (Grade III) or dedifferentiated chondrosarcomas are highly aggressive and carry a much poorer prognosis. For both tumor types, the staging and grading information determines whether the disease is localized, regionally advanced, or metastatic, forming the basis for survival estimates.
Treatment Options and Their Effect on Longevity
The primary goal of curative treatment for sacral sarcomas is complete, surgical removal of the entire tumor in one piece, known as en bloc resection. Achieving a clear margin (R0 resection)—meaning no cancer cells are found at the edge of the removed tissue—is the most important factor influencing long-term local control and potential for cure. This is challenging because the sacrum lies near the spinal canal, major blood vessels, and the S1/S2 nerve roots, which control bladder, bowel, and lower limb function.
The extent of sacral removal often dictates the functional outcome, as sacrificing the S1 or S2 nerve roots can lead to motor deficits or loss of sphincter control. This complexity requires a highly specialized, multidisciplinary surgical team to balance the need for clear margins against preserving neurological function. Failure to achieve an R0 margin (R1 or R2 resection) drastically increases the risk of local recurrence, which is the most common reason for treatment failure and eventual death.
Radiation therapy plays a substantial role, often used in addition to surgery to eliminate microscopic disease, or as the primary treatment if surgery is not feasible. Chordoma and some chondrosarcomas are relatively resistant to standard photon-based radiation. Advanced techniques like high-dose proton therapy or carbon ion radiotherapy are preferable because they allow a higher, more effective dose to be delivered directly to the tumor while sparing nearby structures. Conventional systemic therapies, such as chemotherapy, are rarely effective against these tumors and are typically reserved for cases with aggressive histology or widespread metastasis.
Prognosis and Survival Rates
Survival for sacral cancer varies widely and is directly linked to the tumor type and the stage at diagnosis. For patients with sacral chordoma, overall survival rates are measured over a longer period due to the tumor’s slow growth. Studies report 5-year overall survival rates typically ranging from 62% to 88.3%. However, 10-year survival rates are significantly lower (26% to 59.6%), reflecting the high rate of local recurrence over time, which can reach over 50%.
For sacral chondrosarcoma, the long-term outlook is highly dependent on the tumor’s histological grade. Patients with low-grade (Grade I) chondrosarcoma have an excellent long-term prognosis, with 5-year overall survival rates as high as 97% and 10-year rates around 92%. Conversely, high-grade (Grade III) chondrosarcomas or those in the axial skeleton have worse outcomes, with 5-year survival rates in some cohorts dropping to around 77%.
The most significant factors modifying life expectancy for both tumor types are controllable by treatment. Achieving an R0 surgical margin significantly reduces the risk of local recurrence and improves long-term survival. Tumor size is also a major predictor, with tumors larger than 5 to 8 centimeters consistently associated with a worse overall survival.
The presence of distant metastasis (M1 disease) at diagnosis is the most unfavorable prognostic factor, dramatically reducing the 5-year survival rate for high-grade sarcomas to below 20% in some reports. The tumor’s location within the sacrum also matters. Involvement of the upper sacrum (S1 or S2 vertebrae) makes achieving a clear margin more difficult due to the proximity of nerve roots, which negatively impacts survival. Patient-specific factors such as older age at diagnosis and overall health status are also associated with a reduced overall survival.