Abstract 1926P
Background
Medullary thyroid carcinoma (MTC) is a rare tumor originating from parafollicular C cells. It has more aggressive biologic behavior than differentiated thyroid carcinomas and it is insensitive to treatment with radioactive iodine. Vandetanib and cabozantinib are the new approved tyrosine kinase inhibitors in advanced stages but novel effective systemic therapeutics could be crucial and needed for the clinical management of these patients. In this study we aimed to evaluate the PD-L1 expression, which is a novel immunotherapy target in our MTC patients and its association with clinicopathological characteristics.
Methods
This retrospective study involved 41 cases of MTC with a median follow- up of 54 months. PD-L1 monoclonal antibody (SP263 clone) was investigated by immunohistochemically. Complete and/or partial membranous staining pattern in more than 1% of tumor cells was considered positive. The correlations of PD-L1 expression with clinicopathologic and prognostic features were also analyzed.
Results
PD-L1 positivity of tumor cells was detected in 5 (12.2%) of 41 tumors. The extent of the PD-L1 staining was low (<5%) for all tumors. There was no clinicopathologic and prognostic relevance regarding PD-L1 expression in our MTC patients.
Conclusions
Although PD-L1 expression could be a potential biomarker to predict the prognosis of various cancers and response to checkpoint inhibitors, we did not find any significant correlation between PD-L1 expression and clinicopathologic features in our cases. Studies with larger patient numbers are still required to perform a more comprehensive analysis. Table: 1926P
| Variables | PD-L1 | Total | P-value | |
| Negative | Positive | |||
| Age | ||||
| <50 | 19 (82.6%) | 4 (17.4%) | 23 | 0.363 |
| ≥50 | 17 (94,4%) | 1 (5,6%) | 18 | |
| Sex | ||||
| Female | 20 (83.3%) | 4 (16.7%) | 24 | 0.382 |
| Male | 16 (94.1%) | 1 (5.9%) | 17 | |
| Multiplicity | ||||
| No | 20 (83.3%) | 4 (1.7%) | 24 | 0.382 |
| Yes | 16 (94.1%) | 1 (5.9%) | 17 | |
| Margin | ||||
| Negative | 30 (85.7%) | 5 (14.3%) | 35 | 0.433 |
| Positive | 6 (100.0%) | 0 (0.0%) | 6 | |
| pT stage | ||||
| T1 | 21 (91.3%) | 2 (8.7%) | 23 | 0.554 |
| T2 | 13 (81.3%) | 3 (18.8%) | 16 | |
| T3 | 2 (100.0%) | 0 (0.0%) | 2 | |
| T4a-b | 0 (0.0%) | 0 (0.0%) | 0 | |
| pN stage | ||||
| N0 | 9 (100.0%) | 0 (0.0%) | 9 | 0.192 |
| N1a | 6 (100.0%) | 0 (0.0%) | 6 | |
| N1b | 4 (66.7%) | 2 (33.3%) | 6 | |
| Nx | 17 (85.0%) | 3 (15.0%) | 20 | |
| Recurrence | ||||
| No | 28 (87.5%) | 4 (12.5%) | 32 | 0.701 |
| Yes | 8 (88.9%) | 1 (11.1%) | 9 | |
| Chronic lymphocytic thyroiditis | ||||
| Yes | 7 (87.5%) | 1 (12.5%) | 8 | 0.683 |
| No | 29 (87.9%) | 4 (12.1%) | 33 |
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
Prof. Mehmet Kefeli.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.