From the present analyses of patients with malignant solitary fibrous tumors of the thorax, cancer stage and cancer-directed surgery of the primary site significantly impact OS and CSS. From Cox regression analyses, increments in stage were associated with a HR of ~1.8 for OS and CSS. Cancer-directed surgery was associated with a HR of 0.3 (>3-fold reduction in deaths) for OS and 0.2 (5-fold reduction in deaths) for CSS. While the actuarial OS and CSS of patients undergoing cancer-directed surgery is similar to those not undergoing surgery beyond 5-6 years (), the small number of patients evaluable at these time points (particularly those not undergoing surgery) precludes any definitive conclusions about these findings. Certainly, select patients whose tumors are not resected can experience a prolonged survival.
Malignant solitary fibrous tumors are generally larger than benign tumors (6)
, significantly so in some studies (8)
, though very large tumors can be benign. Perhaps larger tumors are more likely to have undergone genetic changes (13)
. While tumor size has been shown to be prognostic in retrospective series of patients with benign and malignant solitary fibrous tumors (5)
, this study which included only patients with malignant tumors, and others, including benign and malignant histologies (6)
, did not demonstrate an effect of size on survival outcomes.
The survival outcomes reported here are similar to that reported in a Mayo Clinic study (median survival of 4.6 years, and 5-year OS of 46%) which included 11 patients with malignant solitary fibrous tumors (8)
. In a study of 15 patients with malignant solitary fibrous tumors from Memorial Sloan Kettering, the 5-year survival was reported to be 55% (10)
. A Korean study including 13 patients with malignant solitary fibrous tumors reported a median survival of 2.0 years (9)
. A French study reported a 5 and 10-year survival rate of 89% among 22 patients with malignant solitary fibrous tumors (of which only one did not undergo a complete resection) (15)
The observed OS and CSS benefit of cancer-directed surgery for malignant solitary fibrous tumors in this study likely reflects a combination of selection of patients who can tolerate surgery, more indolent disease being amenable to surgical resection and a therapeutic benefit from surgery. The Cox analyses which incorporate stage account for the extent of tumor (albeit with a spectrum of disease extent included within each stage group), and thus there is a possible therapeutic benefit of surgery. Other factors used to select patients for surgery, such as performance status, pulmonary function, cardiac function and comorbid conditions were not accounted for in these analyses, and also likely contribute to the survival benefit of surgery. Because of the retrospective nature of this study, it is not appropriately designed to address how extent of resection impacts outcome, though this data suggests that radical resection results in a trend towards better CSS versus less radical resections. Univariate analyses in this study suggest that undergoing radiation does not significantly impact survival outcomes, although, as described above for surgery, understanding the effect of radiation is complicated by the retrospective nature of this study. Clinical responses to radiation have been reported in the literature for benign (16)
, and malignant solitary fibrous tumors (17)
. The role of adjuvant radiation for solitary fibrous tumors is not known, though it has been suggested that malignant tumors can benefit from adjuvant radiotherapy (3)
Other weaknesses of the present study include the inability to ascertain progression/recurrence free survival and to account for other potentially relevant variables, such as performance status and tumor grade (which is reported in only 16% of patients, despite all having pathologic diagnosis). It must be acknowledged that there are complexities and uncertainties in the pathologic diagnosis of solitary fibrous tumors, which therefore limits the interpretation of retrospective analyses such as this study. It is possible that a pleura mesothelioma or, alternatively, a benign solitary fibrous tumors was misdiagnosed as malignant solitary fibrous tumors. The tumor pathology cannot be systematically reviewed, using modern immunohistochemistry techniques, to verify and specify the pathologic diagnosis. Likewise, radiographic imaging is not available to review, which can also assist in the diagnosis by either CT (18)
or PET criteria (6)
The strengths of the study include the relatively large number of patients analyzed, from an unbiased population-based registry. Analyzing 82 patients allowed investigation of demographic, clinicopathologic and treatment-related variables. Nevertheless, the number of patients (and number of events) is too small to analyze outcomes grouped by stage.