Genomic Landscape and Clonal Hematopoiesis Dynamics in Patients with Ovarian Cancer during PARP Inhibitors Treatment: Preliminary Results of a Prospective Longitudinal Study

Background:

PARP inhibitors (PARPi) are used in epithelial ovarian cancer (EOC) as maintenance therapy in platinum-sensitive patients. However, cytotoxic drug exposure along with PARPi may favor the development of hematological disorders. We recently published a significant increased incidence (8.7%) of therapy related myeloid neoplasms (t-MNs) in women with EOC after a median PARPi treatment duration of 18.5 months. Moreover, using our custom MyeloPanel, we found that patients with clonal cytopenias (CCUS) showed “actionable” mutated genes after PARPi discontinuation. Chemotherapy may also contribute to the increased occurrence of clonal hematopoiesis (CH), an age-related condition, defined by the presence of hematopoietic cells with somatic mutations in genes associated with hematological malignancies, without evidence of disease. We believe that identifying gene mutations that may raise risk for t-MNs in patients treated with PARPi is mandatory.

Aims:

We present preliminary data of a prospective biological study in collaboration among gynecological, hematological and molecular research units at our center.

Methods:

We performed genomic analyses using custom gene panels designed on purpose for assessing germline and clonal hematopoiesis (CH) variants. Germline analyses were conducted on buccal swab DNA at the time of enrolment, while CH analyses on peripheral blood before and every six months post-PARPi therapy. Particularly, for CH, we used high-sensitivity error-corrected sequencing (limit of variant allele frequency, VAF>0.05%), for identification of mutations well below the clinical threshold of 2%.

Results:

To date, we analyzed a total of 46 EOC patients for both germline and CH variants, median age 61.5 years old (min 38-max 85). 55% received olaparib, 30% niraparib and 15% rucaparib. Half of the patients received PARPi in first-line (6 cycles) and the other half in second-line after platinum-based chemotherapy. We found a total of 56 germline variants, 19 (34%) were pathogenic mutations in 18/46 (40%) patients. Of these, 85% were heterozygous mutations in BRCA1/2 genes, strong candidates in the carcinogenic process. Three patients had pathogenic variants in AK2, SLC37A4 and GP1BA genes, not commonly associated with EOC but involved in myeloid malignancies. CH analyses were performed on: 46 patients pre-PARPi, 44 after 6, 14 after 12, 13 after 18 and 6 after 24 months of PARPi treatment. Overall, we identified 392 unique CH-mutations, 63.27% (248/392) were defined as Potential Driver-CH mutations (PD-CH). We observed an increase number of PD-CH mutations per patient by age, consistent with the literature. The most frequently mutated genes were DNMT3A, TP53 and PPM1D, with the majority of CH mutations having a VAF below 2% (91%), highlighting the sensitivity of our sequencing approach. Most patients (96%, 44/46) harboured CH-mutations before PARPi and at least 1 PD-CH mutation. We did not find positive correlations either between PD-CH mutations and patients’ BRCA status, or number of previous cycles of platinum-based chemotherapy. However, we scored a statistically significant co-occurrence of CH mutations in PPM1D and TP53 genes, pattern that persisted overtime. During PARPi treatment, 22/46 (48%) of patients developed CHIP, among which 12 (55%) were characterized by persistent cytopenia, classifiable as CCUS. In these patients, we also scored increasing in VAF of at least one CHIP mutations, particularly evident in PPM1D gene. In general, considering all patients, with long PARPi exposure (up to 2 years), clones with PPM1D seemed to persist and increase over time.

Summary/Conclusion:

Collectively, with our high-sensitivity approach, we observed a high prevalence of CH mutations in EOC patients treated with PARPi. With an increased PD-CH VAF distribution at longer timepoints, particularly evident for clones with PPM1D, our data suggest a possible role of PARPi treatment in the selection of these CH clones. We also observed that prolonged PARPi exposure may increase the risk of CCUS. Furthermore, given the co-occurrence of TP53 and PPM1D mutations, we hypothesize that their interaction may affect the hematopoietic system and potentially contribute to the risk of developing t-MNs.