POLE-ultramutated endometrial cancer

The Cancer Genome Atlas defined the POLE-ultramutated class in 2013: tumours with a hotspot mutation in the exonuclease domain of DNA polymerase epsilon, most often P286R or V411L, which carry more than a hundred mutations per megabase, far more even than mismatch-repair-deficient tumours. About seven percent of endometrial cancers fall into this class. They are more often high grade, endometrioid, with prominent lymphocyte infiltration and ambiguous histology, and they occur in younger, thinner women than the average endometrial cancer patient. Because the pathogenic hotspots are few, a targeted sequencing test settles the class, and the ProMisE algorithm and the WHO 2020 classification both place POLE testing first because a POLE mutation overrides an abnormal p53 or mismatch-repair result.

The defining clinical fact is an excellent outcome regardless of grade or stage. In the molecular analysis of PORTEC-3, women with POLE-ultramutated tumours had almost no recurrences in either arm, so chemotherapy added nothing; the same pattern appeared in PORTEC-1 and PORTEC-2 and in the TransPORTEC pooled cohorts. The ESGO/ESTRO/ESP 2021 guideline therefore lets clinicians omit adjuvant therapy for stage I and II POLE-ultramutated disease, and the RAINBO programme's POLEmut-BLUE trial is testing de-escalation prospectively: no adjuvant treatment for stage I and II tumours and radiotherapy alone for stage III. The rationale is that the ultramutated tumour is intensely immunogenic and any residual cells are cleared by the immune system after surgery.

Open questions are practical rather than therapeutic. Not every POLE variant is pathogenic, and misclassifying a passenger variant as a driver would deny a woman treatment she needs, so laboratories use a curated list of hotspots and a scoring scheme for other variants. The rare advanced or recurrent POLE-ultramutated tumour is expected to respond to checkpoint inhibitors because of its mutational load, but numbers are too small for trials. Universal molecular classification, now routine in the Netherlands, Canada and the United Kingdom, is the step that makes any of this possible, and it is still uneven elsewhere.