MFN are rare malignant tumours. Attention was paid to fibrosarcoma, fibromyxosarcoma, periosteal fibrosarcoma and malignant fibrous histiocytoma.
These tumours can infiltrate adjacent tissues and metastasize distally [13,14,15,16,17,18,19]. However, the outcome and prognosis of patients with MFN of long bones have not been reported because of its rarity. To our knowledge, the current study is the first to report the prognostic factors that affect the survival of patients with MFN of long bones using multivariate regression analysis.
In the current study, we identified 237 cases of malignant fibrous neoplasms of long bone based on the SEER database from 1973 to 2015. The OS and CSS rates at 5 years were 39.7 and 60.3%, respectively, while the previous study results showed that the OS and CSS of sinonasal fibrosarcoma were 71.7 and 77.8%, respectively [13].
Although malignant fibrous histiocytoma (MFH) ceased to be recognised as an entity in the 2013 edition of the WHO classification of bone and soft tissue tumours [20], undifferentiated high-grade pleomorphic sarcoma is listed as a new synonym for MFH of bone, still with the same code 8830/3, in the recently published ICD-O-3.2. However, the registrations of undifferentiated high-grade pleomorphic sarcoma of bone still decreased in the seer database. This might explain the recent decrease in registrations of MFH. Therefore, this study was of more than purely historical interest.
Survival by age
We observed different survival rates by age at diagnosis in many studies [14]. In contrast, we found a higher risk of poor OS in the elder group. In the multivariate analysis of OS for patients aged 17–39 years the HR was 2.765 (P = 0.098), for those aged 40–60 years the HR was 3.81 (P = 0.027), and for those aged > 60 years the HR was 5.688 (P = 0.004). We also found a higher risk of poor CSS in the elder group. In the multivariate analysis of CSS for those aged > 60 years, the HR was 3.863 (P = 0.03*).
Survival by gender, race and decade of diagnosis
Our results were consistent with previous results where no differences in survival by gender, or race but not decades were founded [21]. The differences of decades might be caused by the primary site of long bone or small bone.
Survival by radiotherapy and chemotherapy
Radiotherapy was used as an adjunct to surgical management in patients with positive margins [22]. In the univariate analysis of OS, radiotherapy (RT) was associated with poor CSS (HR was 1.652(P = 0.02)) and OS (HR was 1.684(P = 0.003)). The results were consistent with a recent study [15]. This may be caused by the selection bias of patients with radiotherapy. Chemotherapy was also an important adjuvant therapy. In the multivariate analysis of OS and CSS, we did not find that chemotherapy was an independent prognostic factor for OS and CSS. However, a previous study demonstrated that clinical factors were associated with radiotherapy only in nonmetastatic malignant fibrous histiocytoma (MFH) of soft tissues [1].
Survival for tumour type and tumour sequence
Tumour type was not an independent prognostic indicator for OS or CSS in multivariate analysis. In addition, tumour sequence was an independent prognostic indicator of OS and CSS, suggesting that patients with second primary bone MFN in their long bones may have a worse prognosis than those with a first primary tumour. The patients’ number of more than 2 sequence was as low as 29, among which 12 in fibrosarcoma, 17 in malignant fibrous histiocytoma. This leads to the difficulty in analyzing in multivariate analysis. Therefore, the results of tumour sequence should be taken into consideration carefully.
Survival by tumour size
For smaller tumours with no evidence of metastasis, surgical extirpation alone may be the definitive treatment [16, 23]. Our study showed that tumour size > 10 cm was a prognostic factor for both poor OS and CSS, which was consistent with a recent study [16].
Survival for stage and surgery
Stage and surgery have been previously recognized as predictors of survival in patients with malignant bone tumours [24,25,26]. These factors were also independent predictors of OS and CSS in the study. MFN was highly metastatic tumour. Therefore, surgical removal of the primary tumour and distant lesions should be addressed and may be applicable to prolong survival in patients with MFN of the long bones and metastasis at diagnosis. Surgery remains the primary treatment strategy for MFN. Patients treated with this strategy had the best OS and CSS. Finally, there was not significant difference between upper limbs and lower limbs (data not shown).
Strengths and limitations
This study is a population-based, with high-quality data, and the largest ever published on this category of rare tumours. However, this study has several limitations. These include the fact that there were no data on surgical type, node status, and RT dose.