Tissue Heterogeneity as a Pre-analytical Source of Variability

Intratumoral Heterogeneity in Differentiated Thyroid Tumors: An Intriguing Reappraisal in the Era of Personalized Medicine

Differentiated thyroid tumors (DTTs) are characterized by significant molecular variability in both spatial and temporal intra-tumoral heterogeneity (ITH), that could influence the therapeutic management. ITH phenomenon appears to have a relevant role in tumor growth, aggressive behavior and drug resistance. Accordingly, characteristics and consequences of ITH in DTTs should be better analyzed and understood in order to guide clinical practice, improving survival. Consequently, in the present review, we investigated morphological and molecular ITH of DTTs in benign, borderline neoplasms and in malignant entities, summarizing the most significant data. Molecular testing in DTTs documents a high risk for recurrence of cancer associated with BRAF^V600E, RET/PTC 1/3, ALK and NTRK fusions, while the intermediate risk may be related to BRAF^K601E, H/K/N RAS and PAX8/PPARγ. In addition, it may be suggested that tumor genotype is associated with peculiar phenotype.

Validity of whole genomes sequencing results in neoplasms in precision medicine

OBJECTIVE

To compare the whole genomes sequencing (WGS) results in the 100K Genomes project with the results of routine molecular diagnostics in precision medicine.

MATERIALS AND METHODS

We analysed 374 cancers including a high tumour mutational burden (TMB-high) subgroup, defined as >10 non-synonymous single nucleotide variations per megabase. Colon cancers were evaluated for microsatellite instability (MSI), mismatch repair (MMR) genes and NRAS, KRAS and BRAF mutations using routine molecular diagnostics. Fluorescence in-situ hybridisation/immunohistochemistry was used to evaluate the Her2Neu status in breast cancers.

RESULTS

There was high correlation between WGS and routine diagnostic testing results irrespective of TMB status in colon cancers. Her2Neu status was discordant in 3 out of the 5 TMB-high breast cancers (p=0.049). The presence of ductal carcinoma in-situ correlated significantly with discordance (p=0.04). There were 3 (5%) discordant colorectal cases, all in the KRAS gene, 2 of which were from the non-invasive adenomatous component (p=0.0058). Of the 374 cases we identified 24 tumours with a TMB >10; comprising (colorectal carcinomas (CRCs) n=16, breast carcinomas n=5, bladder urothelial cell cancers n=3). Of the 16 TMB-high colorectal adenocarcinomas, 13 had MSI-high status. The same 13 had defective MMR protein expression. TMB-high colorectal cancers had 100% concordant results between WGS and NGS testing for KRAS, BRAF and NRAS (16/16).

CONCLUSION

The microsatellite and mutational status of colorectal cancers evaluated by WGS seem to correlate well with the routine diagnostic testing if it is ensured that the invasive component is sequenced. Evaluation of WGS results need to be carefully correlated with histomorphology, as tumour heterogeneity/contamination with pre-malignant components needs to be taken into account.

Overview on Clinical Relevance of Intra-Tumor Heterogeneity

Today, clinical evaluation of tumor heterogeneity is an emergent issue to improve clinical oncology. In particular, intra-tumor heterogeneity (ITH) is closely related to cancer progression, resistance to therapy, and recurrences. It is interconnected with complex molecular mechanisms including spatial and temporal phenomena, which are often peculiar for every single patient. This review tries to describe all the types of ITH including morphohistological ITH, and at the molecular level clonal ITH derived from genomic instability and nonclonal ITH derived from microenvironment interaction. It is important to consider the different types of ITH as a whole for any patient to investigate on cancer progression, prognosis, and treatment opportunities. From a practical point of view, analytical methods that are widely accessible today, or will be in the near future, are evaluated to investigate the complex pattern of ITH in a reproducible way for a clinical application.

Heterogeneity of Thyroid Cancer

There are 5 main histological types of thyroid cancers (TCs): papillary, follicular (also known as differentiated), poorly differentiated, anaplastic (the most aggressive form), and medullary TC, and only the latter arises from thyroid C cells. These different forms of TCs show significant variability, both among and within tumours. This great variation is particularly notable among the first 4 types, which all originate from thyroid follicular cells. Importantly, this heterogeneity is not limited to histopathological diversity only but is also manifested as variation in several genetic and/or epigenetic alterations, the numbers of interactions between the tumour and surrounding microenvironment, and interpatient differences, for example. All these factors contribute to the great complexity in the development of a tumour from cancer cells. In the present review, we summarise the knowledge accumulated about the heterogeneity of TCs. Further research in this direction should help to gain a better understanding of the underlying mechanisms contributing to the development and diversity of TCs, paving the way toward more effective treatment strategies.

Tumour heterogeneity: principles and practical consequences

Two major reasons compel us to study tumour heterogeneity: firstly, it represents the basis of acquired therapy resistance, and secondly, it may be one of the major sources of the low level of reproducibility in clinical cancer research. The present review focuses on the heterogeneity of neoplastic disease, both within the primary tumour and between primary tumour and metastases. We discuss different levels of heterogeneity and the current understanding of the phenomenon, as well as imminent developments relevant for clinical research and diagnostic pathology. It is necessary to develop new tools to study heterogeneity and new biomarkers for heterogeneity. Established and new in situ methods will be very useful. In future studies, not only clonal heterogeneity needs to be addressed but also non-clonal phenotypic heterogeneity which might be important for therapy resistance. We also review heterogeneity established in major tumour types, in order to explore potential similarities that might help to define new strategies for targeted therapy.