Linear mixed-effects models for predicting sarcoma local recurrence growth rates: Implications for optimal surveillance imaging frequency.

PURPOSE

Sarcomas are rare tumours of mesenchymal origin that are often treated with surgical resection and radiation to prevent local recurrence (LR). Surveillance for LR after surgical resection is often done with contrast-enhanced MRI, however, the optimal frequency of surveillance imaging is unknown. The aims of this study are to calculate LR growth, and to evaluate the factors that affect LR growth and to use this data to predict the optimal imaging surveillance frequency.

METHOD

Retrospective cohort study of patients with sarcoma who were treated at a tertiary care academic institution between 01/01/2007 and 01/03/2020 identified 34 patients with 60 histologically confirmed LRs. The maximum LR length was measured on each surveillance MRI. Linear mixed-effects models were used to calculate the maximum LR length growth rate. We evaluated whether age, sex, primary sarcoma tumour size, sarcoma grade, margins, chemotherapy or radiation therapy affected the growth rate of the maximum LR length.

RESULTS

One patient had 6 LRs (2.9 %), two patients (5.9 %) had 5 LRs, two patients (5.9 %) had 4 LRs, two patients (5.9 %) had 3 LRs, three patients (8.8 %) had 2 LRs, and twenty-four patients (70.6 %) had 1 LR. Most patients had high grade (Grade II/III) disease (88.2 %). 41.2 % of the patients had microscopically positive surgical margins. The median time (range) from surgery to LR was 264 days (17 - 8013) days, and 90 % occurred within 42.8 months (1284 days). Microscopically positive margins were associated with faster growth of the maximum LR length (P = 0.036). Assuming that a 1 cm sarcoma LR is actionable and that the previous surveillance MRI was negative, the data predicts that patients with microscopically positive margins should have surveillance MRIs every 6.2 months when LRs are expected to achieve a length of 1.0 cm (95 % CI (0.4-2.3 cm)).

CONCLUSIONS

Patients with microscopically positive resection margins had LRs that grew faster than patients with negative margins. Surveillance imaging with contrast-enhanced MRI could be conservatively performed every 6 months when LRs are expected to be just less than 1.0 cm in length.