Introduction/Background Maintenance with PARP inhibitors (iPARP) has become standard of care for patients suffering from high-grade serous ovarian cancer (HGSOC). Patients harbouring germline BRCA1/2 mutations responding to platinum-based chemotherapy benefit the most from iPARP. Treatment with iPARP can rarely be associated with severe long-term toxicities including myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML).

Methodology A 74-year-old patient with stage FIGO IIIC HGSOC was treated with six cycles of carboplatinum and paclitaxel chemotherapy, interval macroscopically complete surgical cytoreduction, followed by a two-year maintenance treatment by olaparib. One month after completion, she complained of severe fatigue, shortness of breath and palpitations.

Results She was diagnosed with severe microcytic anaemia, mild lymphocytopenia and normal platelet count. The injected thoraco-abdominal and pelvic CT-scan ruled out interstitial lung disease, HGSOC recurrence and other primary malignant localization notably without liver nor lymph node involvement. Further haematological workup detected iron-deficient regenerative anaemia and the blood smear ruled out an MDS/AML. The endoscopic gastrointestinal assessment by gastroscopy and colonoscopy detected an ulcerated right colic tumour with active bleeding. The patient underwent laparoscopic right colectomy. The pathological assessment confirmed a grade 3, pT2 pN0 (0/17) cM0, sporadic mismatch deficient (dMMR), intestinal adenocarcinoma, harbouring a c.1799T>A (p.Val600Glu) exon 15, BRAF mutation.

Conclusion This report underlines the importance of a comprehensive differential diagnosis for blood-associated toxicities in the aftermath of iPARP maintenance treatment, especially among the BRCA1/2 mutant patients. Interestingly the dMMR colic tumour did not harbour BRCA1/2 mutation by Next Generation Sequencing.