1763P - Initial tumour size and residual mitotic count post-neoadjuvant imatinib linked to shorter relapse-free survival in GIST patients

Background

In locally advanced GIST patients, neoadjuvant (NA) imatinib facilitates surgery and allows in vivo monitoring of tumour response to therapy. This study evaluated in this population the impact of clinicopathological variables, including initial tumour size (ITS) and residual mitotic count (RMC) after NA imatinib, on relapse-free survival (RFS).

Methods

Single-center retrospective study of 69 patients with sensitive mutations treated with NA imatinib who underwent radical surgery for localized disease. The RMC was determined per 5 mm² in the surgical specimen. RFS was defined as the time from surgical treatment to disease relapse. Univariate and multivariate Cox regression analyses were performed to determine the association of clinicopathological variables to RFS, and are reported as Hazard Ratio (HR) and 95% confidence intervals (CIs). We used Evaluate Cutpoints to identify the optimal value of ITS and RMC associated with significantly different outcomes.

Results

Most tumours arose from the stomach (62.3%) and carried a KIT exon 11 mutation (78.3%). Median ITS was 9.4 cm. After NA treatment, RMC was found in the surgical specimen of 31 (44.9%) patients (Table). Of all the variables tested, univariate Cox regression analyses showed a significant association of RFS with ITS (HR 1.15 [95% CIs 1.06-1.25], p < 0.001) and RMC (HR 1.04 [95% CIs 1.02-1.06], p = 0.001). These results were confirmed in a multivariate model (ITS, HR 1.15, 95% CIs 1.06-1.25, p = 0.001; RMC, HR 1.04, 95% CIs 1.01-1.06, p = 0.002). A combined score of these variables after optimal dichotomization performed with Evaluate Cutpoints is able to correctly separate 3 risk categories (p < 0.001). Table: 1763P

General characteristics

Conclusions

ITS and RMC are associated with shorter RFS in patients with localized GIST treated with NA imatinib. If validated, these findings could guide the design of prospective studies that de-escalate or intensify adjuvant treatment depending on these variables.

Clinical trial identification

Editorial acknowledgement

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.