Rate of p53 and MMR IHC assessment accordance between matched D&C and hysterectomy samples in uterine cancer.

e17587 Background: International guidelines strongly suggest assessment of POLe, MMR, p53 in patients with early stage endometrial cancer. MMR and p53 are commonly assessed with IHC after hysterectomy (+/-BSO). The fixation procedure and the high tumor cellularity of D&C specimens may permit accurate p53 and MMR evaluation. Early knowledge of p53 and MMR status in D&C samples may drive surgical treatment modalities and fertility sparing decision. Methods: In this single center study 73 matched D&C and hysterectomy samples in patients with clinically early stage endometrial cancer were collected and p53 and MMR status was assessed with IHC.Samples were obtained by gynaecologists and gynaecological oncologists and independently assessed by two expert in gynaecological oncology pathologists at REA hospital (Athens-Greece).Immunohistochemistry was performed using Ventana Benchmark Ultra. To determine MMR status, sections were scored visually for loss or intact expression of the proteins MSH6, MSH2, MLH1 and PMS2. Interpretation of immunostaining for each protein was classified as: (i) “retained,” when ≥10% of tumor cells showed a moderate to strong expression; (ii) “loss,” when no evidence of nuclear expression was seen in cancer cells; (iii) “indeterminate,” if IHC staining in tumor cells was less intense compared to the internal control or expression was retained in <10% of neoplastic cells.If, however, the presence of “indeterminate” immunostaining in one or more proteins was coupled with a convincing loss of expression in at least one protein, the tumor was interpreted as “dMMR” tumor.The study was carried out within January 1 st -December 1 st 2023. Results: There was a 100% accordance between p53 assessment in all 73 matched D&C and hysterectomy specimens. Discrepancy in MMR result was observed only in 1 out of the 73 cases, which stained negative for MLH1 in D&C but positive in hysterectomy, yielding an accordance of 98,96% between D&C and hysterectomy specimens. Conclusions: p53 & MMR status can be accurately assessed with IHC in D&C samples. Repeat assessment after hysterectomy may not be necessary. Early knowledge of the molecular imprint of the disease on D&C samples may drive treatment decisions regarding surgical procedures, fertility preservation and further treatment plans. [Table: see text]