Sarcomas are a heterogeneous group of malignant tumors of mesenchymal origin (1–3). They are relatively rare, representing less than 1% of all adult malignancies and 12% of pediatric malignancies (1, 2). Sarcomas can occur at all anatomic sites in the body, but the majority are in the extremities (2). A study reviewed the anatomic distribution of soft tissue sarcomas in 4,550 adults, 46% of them occurred at thigh, buttock, and groin, 13% occurred at upper extremity, torso and retroperitoneum accounted for 18% and 13% respectively, while head and neck only constituted 9% (4). The care for patients with sarcomas is usually based on anatomic site and histology, so there is no unified treatment standard.

The majority of primary testicular tumors derive from germ cell origin. Primary testicular sarcoma (TS) is particularly rare. Since it differs from primary testicular germ cell tumors (TGCT), the risk assessment system currently used for testicular tumors shall not be applicable for TS.

As far as we know, a number of cases of TS have been reported in the previous literature (5–18), but no cohort study has been published. This study aimed to identify the clinical characteristics and factors that may affect the prognosis of TS patients. This study was based on information from the National Cancer Institute’s Surveillance Epidemiology and End Results (SEER, RRID: SCR_006902) database (2006–2016).

Sarcomas are complicated malignancies encompassing a broad histopathologic spectrum. Approximately 80 percent of new cases of sarcomas originate from soft tissue, and the rest originate from bone (1, 2). As classified by the fourth edition of the World Health Organization (WHO), there are more than 100 different histologic subtypes of soft-tissue neoplasms (3, 19). Histologic grade is currently recognized the most important prognostic factor for sarcomas and is predictive of distant metastasis and cancer-specific survival (2, 3). There are several grading systems. The AJCC Staging System uses a four-grade scheme ranging from G1 (well-differentiated) to G4 (undifferentiated) (20). The French Federation of Cancer Centers Sarcoma Group (FNCLCC) grading schema, basing on three parameters: differentiation, mitotic rate, and necrosis, is widely recommended (2, 20, 21). In addition to histologic grade, tumor size and pathologic stage at the time of diagnosis are counted as another two most important prognostic factors (2).

Due to the histological difference between TS and TGCT, the clinical and pathological characteristic of TS may differ from TGCT. The management decision of TS should not be made on the basis of current guidelines for testicular tumors (which was mainly on TGCTs). Since TS is particularly rare, studies about this cancer are limited, and most of them are case reports or case reviews (5–18). To our knowledge, this is the first cohort study based on a relatively large amount of TS patients, reporting clinical characteristics and factors that may affect the prognosis of TS patients.

As reported in our study, patients with distant metastasis had a 17.86 fold increased risk to die of TS itself [OR = 17.86, 95% CI (4.63–68.84), p < 0.0001], and patients with T3 disease had a 4.13 fold increased risk [OR = 4.13, 95% CI (1.10–15.53), p = 0.0359]. The risk of DM in patients with advanced T stage was higher than those with lower T stage, 13.91 fold (95% CI, 1.80 to 107.54 fold) for T3 and 16.36 fold (95% CI, 1.36 to 196.21 fold) for T4. We can conclude that necessary imaging techniques should be used to evaluate the extent of a primary tumor and to establish the presence or absence of metastatic disease. For those patients with metastasis or advanced T stage disease, further treatment and comprehensive management should be formulated. At present there are no relevant guidelines regarding retroperitoneal lymph node dissection (RPLND) in TS patients. For retroperitoneal sarcomas, the cornerstone of treatment is surgical resection (3). So we consider RPLND necessary when imaging shows enlarged retroperitoneal lymph nodes.

Patients with Grade II disease had a 14.29 fold increased risk of LM [OR = 14.29, 95% CI (1.41–144.36), p = 0.0242], and patients with Grade IV disease had a 9.19 fold increased risk of DM [OR = 9.19, 95% CI (1.02–82.42), p = 0.0476] before adjustment. However the difference became not statistically significant after adjustment. In addition, we did not find there were statistical difference when evaluating the impact of differentiation grade and surgery on CSM, the impact of tumor size on CSM, LM, and DM. These findings may be due to the small sample size and the variability in the number of patients of different T stages and differentiation grades. We can still speculate from the Kaplan-Meier curve that the survival rate of TS patients lowered with worse differentiation, though this difference was not statistically significant (p > 0.05).

What’s more, most patients enrolled in our study had normal AFP, hCG, and LDH. This is consistent with previously reported cases, including but not limited to a 27-year-old male with high-grade primary testicular leimyosarcoma reported by Fouzia Siraj et al. (5) and a 51-year-old patient with primary testicular sarcoma reported by Allaway M. et al. (6). We did not find that these serum tumor markers had a statistically significant impact on CSM and DM in TS patients. Unlike in germ cell tumors, where elevations of tumor markers (AFP, hCG, and LDH) allow for staging and determination of treatment regimen, no known marker exists in TS. Future work may elucidate a prognostic biomarker for TS.

Although this is the first cohort study in TS, there are limitations of our study. Due to its retrospective nature, not all clinical data were collected in SEER database, which is a common defect in any observational study. In addition, because of the limited size of the study cohort, some outcomes were not adequately powered to detect a statistical significance. As there are no guidelines for the diagnosis and management of patients with TS, there was likely high variability in the staging and receipt of imaging as well as treatments received by the patients in this cohort.

According to our study, patients with advanced T stage were more likely to have distant metastasis. Both distant metastasis and advanced T stage were associated with worse CSM. The recognization of these poor prognostic factors may allow physicians to make comprehensive and appropriate management decision for TS patients. In order to better understand this disease, larger powered studies are needed.

The original contributions presented in the study are included in the article/ Supplementary Material . Further inquiries can be directed to the corresponding author.

Ethical review and approval was not required for the study on human participants in accordance with the local legislation and institutional requirements. Written informed consent from the participants’ legal guardian/next of kin was not required to participate in this study in accordance with the national legislation and the institutional requirements.

(I) Conception and design: XW, ZC, and SQ. (II) Administrative support: YB, LY, LL, and QW. (III) Provision of study materials or patients: XW, ZC, SQ, and KJ. (IV) Collection and assembly of data: XW, ZC, JL, BC, HL, and YH. (V) Data analysis and interpretation: XW, ZC, SQ, KJ, and YB. (VI) Manuscript writing: XW, ZC, SQ, DC, KJ, JL, BC, HL, YH, YB, LY, LL, and QW. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.