Does HUMARA assay for assessment of clonal hematopoiesis have shortcomings?

Pleomorphic adenoma: Detection of PLAG1 rearrangement-positive tumor components using whole-slide fluorescence in situ hybridization

AIM

Pleomorphic adenoma (PA) consists of heterogeneous histological architecture mixed with epithelioid and mesenchymal forms. Various types of epithelial or myoepithelial malignancies arise from PA, but sarcomas are extremely rare. A HUMARA clonality assay has suggested that PA is clonal in nature. However, clonality of various tumor components of PA would be difficult to determine with this assay. In addition, the results obtained should be carefully interpreted. PLAG1 rearrangements are considered a good molecular marker for neoplasticity in PA. We aimed to clarify the neoplasticity of the various tumor components present in PA using whole-slide fluorescence in situ hybridization (FISH).

METHODS

Five PA cases positive for PLAG1 rearrangements were examined. Using an immunohistochemistry panel, cell components in PA were classified into eight cell types. To precisely localize PLAG1 rearrangement-positive cell components at the cellular level, sequential retrieval of whole-slide imaging (WSI) data of HE histology and FISH for PLAG1 rearrangement was carried out.

RESULTS

PLAG1 rearrangements were detected in ductal cells, myoepithelial spindle cells, myoepithelial oncocytic cells, myoepithelial plasmacytoid cells, and mesenchymal chondroid cells, but not in mesenchymal lipid cells, mesenchymal fibrous cells, or vascular endothelial cells. Immunohistochemical PLAG1 expression was restricted to cell components harboring PLAG1 rearrangements.

CONCLUSIONS

The results of the present study indicate that ductal and myoepithelial, chondroid cells are neoplastic but lipid, fibrous, and endothelial cells are not. PLAG1 immunohistochemistry is useful in discriminating neoplastic from non-neoplastic cell components. These findings may be important for elucidating tumorigenesis and the process of malignant transformation in PA.

Multiclonal tumor origin: Evidence and implications

An accurate understanding of the clonal origins of tumors is critical for designing effective strategies to treat or prevent cancer and for guiding the field of cancer risk assessment. The intent of this review is to summarize evidence of multiclonal tumor origin and, thereby, contest the commonly held assumption of monoclonal tumor origin. This review describes relevant studies of X chromosome inactivation, analyses of tumor heterogeneity using other markers, single cell sequencing, and lineage tracing studies in aggregation chimeras and engineered rodent models. Methods for investigating tumor clonality have an inherent bias against detecting multiclonality. Despite this, multiclonality has been observed within all tumor stages and within 53 different types of tumors. For myeloid tumors, monoclonal tumor origin may be the predominant path to cancer and a monoclonal tumor origin cannot be ruled out for a fraction of other cancer types. Nevertheless, a large body of evidence supports the conclusion that most cancers are multiclonal in origin. Cooperation between different cell types and between clones of cells carrying different genetic and/or epigenetic lesions is discussed, along with how polyclonal tumor origin can be integrated with current perspectives on the genesis of tumors. In order to develop biologically sound and useful approaches to cancer risk assessment and precision medicine, mathematical models of carcinogenesis are needed, which incorporate multiclonal tumor origin and the contributions of spontaneous mutations in conjunction with the selective advantages conferred by particular mutations and combinations of mutations. Adherence to the idea that a growth must develop from a single progenitor cell to be considered neoplastic has outlived its usefulness. Moving forward, explicit examination of tumor clonality, using advanced tools, like lineage tracing models, will provide a strong foundation for future advances in clinical oncology and better training for the next generation of oncologists and pathologists.

Distinguishing myelodysplastic syndromes (MDS) from idiopathic cytopenia of undetermined significance (ICUS): HUMARA unravels clonality in a subgroup of patients

BACKGROUND

Patients not fulfilling minimal criteria for myelodysplastic syndromes (MDS) but presenting with persisting cytopenia(s) not attributable to a haematological or non-haematological disease are defined as 'idiopathic cytopenia of undetermined significance' (ICUS).

DESIGN AND METHODS

We retrospectively analysed 67 of 3504 patients from our MDS Registry fulfilling the criteria for ICUS. Furthermore, we used the human androgen receptor gene-based assay (HUMARA) to look for clonality.

RESULTS

Of all 67 patients, 66% had unilineage, 18% bilineage and 12% trilineage cytopenias. The majority of patients (67%) presented with anaemia. Median overall survival was 44 months (range: 1-199 months). In the entire group, eight patients (12%) developed acute myeloid leukaemia (AML). Of the 23 patients eligible for HUMARA, 17 had non-clonal X-chromosome inactivation patterns, while 6 patients showed clonal patterns. Two of these six patients developed AML indicating that a clonal stem cell disorder was the reason for the anteceding cytopenia, while there was no AML observed among the 17 patients with non-clonal patterns (P = 0.013).

CONCLUSIONS

Since some of the ICUS patients had a clonal bone marrow disease when presenting with cytopenia(s) and 8 of 67 patients with ICUS later developed AML, we recommend to follow these patients thoroughly. As demonstrated here, HUMARA can facilitate the discrimination between ICUS and a 'manifest' MDS.