# High Burden of Non-Clonal Chromosome Aberrations Before Onset of Detectable Neoplasia in Fanconi Anemia Bone Marrow

## TL;DR

This study reveals that non-clonal chromosome changes are common in Fanconi anemia bone marrow before cancer develops, suggesting a stepwise progression toward malignancy.

## Contribution

The study provides new insights into the preleukemic cytogenetic landscape in Fanconi anemia, highlighting the role of non-clonal chromosomal abnormalities.

## Key findings

- Non-clonal chromosomal abnormalities (NCCAs) were present in 41 out of 43 Fanconi anemia patients.
- Complex karyotypes and clonal chromosomal abnormalities (CCAs) emerged later, often involving chromosomes 1, 3, and 7.
- Karyotypic heterogeneity precedes the selection of cancer-associated clones in Fanconi anemia.

## Abstract

Fanconi anemia (FA) is the most common inherited bone marrow failure syndrome, characterized by chromosomal instability and a high risk of cancer. Hematologic malignancy in FA, mainly myelodysplastic neoplasm (MDS) and acute myeloid leukemia (AML), associates with characteristic clonal chromosomal abnormalities in the bone marrow. Although clonal chromosome abnormalities (CCAs) associated with malignant progression in FA involve chromosomes 1, 3, and 7, information on the broader preleukemic bone marrow cytogenetic landscape is scarce. In this study, we report the type and frequency of every kind of non-clonal chromosomal abnormality (NCCA) appearing in the bone marrow of a group of patients with FA, spanning from cancer-free patients to hematologic malignancy, where CCA appears. This study unveils the dynamism of emerging karyotypes in the FA bone marrow and its potential association with the patient’s hematological state.

Background/objectives: Fanconi anemia (FA) is an inherited bone marrow failure syndrome characterized by chromosome instability and predisposition to develop myelodysplastic neoplasm (MDS) and acute myeloid leukemia (AML). Clonal chromosome aberrations (CCAs) in chromosomes 1, 3, and 7 frequently appear in the bone marrow (BM) of patients with FA and are associated with MDS/AML progression. Given the underlying DNA repair defect that characterizes FA, non-clonal chromosomal abnormalities (NCCAs) are expected to be common events in the FA BM; in this study, we investigated the presence and significance of NCCA and CCA in the bone marrow (BM) of patients with FA. Methods: Here, we transversally examined the BM karyotypes of 43 non-transplanted patients with FA, 41 with non-clinically detectable hematologic neoplasia and two with diagnosed MDS. We searched for the presence of NCCAs, complex karyotypes (CKs), and CCAs as well as their association with the natural history of the disease, including age, degree of BM failure, and neoplastic transformation. Results: NCCAs were observed in the metaphase spreads of 41/43 FA patients; CKs were observed in 25/43 patients; CCAs were found in 15/43 patients; CCAs involving chromosomes 1, 3 and/or 7 were found in four patients; and other autosomes were found in the remaining 11 patients. Overall, we observed a baseline large karyotypic heterogeneity in the BM of FA patients, demonstrated by the ubiquitous presence of NCCA; such karyotypic heterogeneity precedes the eventual emergence of CKs and selection of cells carrying fitness-improving CCAs. Finally, CCAs involving chromosomes 1, 3 and 7, well-known drivers of hematological malignancy in FA, become established. Overall, we observed that the frequency of NCCAs and CCAs increased with age, even though a significant correlation was not found. Conclusions: These observations fit the model of evolution towards cancer that comprises a first phase of macroevolution represented by NCCAs and karyotypic heterogeneity, followed by the establishment of clones with CCAs, leading to microevolution and cancer. NCCAs are the most frequent chromosomal alterations in the bone marrow of patients with AF and constitute a genome with extensive karyotypic heterogeneity that evolves into clones with more complex genomes and can eventually progress to cancer.