(P 192) ROLE OF MAGNETIC RESONANCE IMAGING IN THE PREDICTION OF HISTOLOGICAL GRADE IN SOFT TISSUE SARCOMAS.

Objective: This study aims to assess the role of pre-operative Magnetic Resonance Imaging (MRI) in predicting the histological grade of non-metastatic soft tissue sarcoma.

Methods: This is an observational, cross-sectional retrospective single center study. The inclusion criteria consisted of patients over 18 years old who underwent guided core needle biopsy or external pathologic diagnosis review, MRI examination, and primary tumor surgery at the ACCCC between January 2015 and June 2022. Patients who underwent surgical biopsy were excluded. The main variables included age, tumor size, location, histological subtype, histological grade of the biopsy and surgical specimen (categorized as high grade for G2 and G3 and low grade for G1 of the FNCLCC classification). Two radiologists from our institution evaluated MRI radiological criteria such as size, margin definition (regular or irregular), heterogeneity of the T2 signal (greater than 50% or less than 50%), high intensity peritumoral signal on T2 (presence or absence of peritumoral edema), and peritumoral post-contrast enhancement (presence or absence). Additionally, a score was calculated to assess the prediction of histological grade by summing the positive criteria analyzed (ranging from 0 (zero) when no criteria were identified to 5 (five) when all criteria were positive). The Chi-square and Fisher’s exact test were employed to examine the relationship between the MRI parameters and the histological grade of the surgical specimen and logistic regression analysis to identify independent associations was performed. A p-value < 0.05 was considered statistically significant.

Results: A total of 68 patients who met the inclusion and exclusion criteria were included in the study, comprising 30 women and 38 men. The biopsy identified 54 high-grade tumors and 14 low-grade tumors. In the surgical specimen, 52 high-grade tumors and 16 low-grade tumors were observed. The most common type of biopsy was ultrasound-guided core needle biopsy, accounting for 54.4% of cases. The most frequent histologies were Liposarcoma (26.4%), followed by synovial sarcoma (17.6%) and leiomyosarcoma (10.3%). The majority of tumors were located in the extremities (64.7%), and tumors larger than 5cm were identified in 89.7% of cases. Margins were regular in 43 (63.2%) cases and irregular in 25 (36.8%) cases. Tumor heterogeneity in T2 was observed in 36 (52.9%) cases compared to 32 (47.1%) cases without heterogeneity. Peritumoral high-intensity T2-weighted signal was present in 45 (66.2%) cases, while peritumoral post-contrast enhancement was present in 31 (45.6%) cases. The scores were as follows: 2 with a score of 0 (zero), 10 with a score of 1 (one), 16 with a score of 2 (two), 13 with a score of 3 (three), 18 with a score of 4 (four), and nine with a score of 5 (five). The MRI criteria that demonstrated an association with histological grade were peritumoral high-intensity T2-weighted signal (p < 0.001) and peritumoral post-contrast enhancement (p = 0.006). Logistic regression analysis indicated that the presence of peritumoral high-intensity T2-weighted signal (OR 11.8, CI 95% 3.0 – 41.5, p < 0.001) and peritumoral post-contrast enhancement (OR 8.8, CI 95% 1.8 - 42.8, p 0.007) were also predictive of high-risk tumors. Although the other MRI criteria were not associated with histological grade, applying the score (sum of the MRI findings) revealed that each additional point doubled the chance of a high-grade tumor (OR 2.0; CI 95% 1.2 – 3.3, p = 0.005).

Conclusion: MRI is an effective tool for predicting the histological grade of soft tissue sarcomas. MRI criteria related to the infiltrative tumor growth pattern, such as peritumoral high-intensity T2-weighted signal and peritumoral post-contrast enhancement, showed positive predictive value for histological high grade. These findings could be helpful in better defining the treatment plan. Further studies should validate our data.