When does a new sarcoma exist?
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(2020) 10:19 Casali et al. Clin Sarcoma Res https://doi.org/10.1186/s13569-020-00141-9
Open Access
EDITORIAL
When does a new sarcoma exist? Paolo G. Casali1,2*, Angelo Paolo Dei Tos3 and Alessandro Gronchi1
Pathologists diagnose cancers by looking at how their morphological, histochemical and molecular characteristics cluster in a single case. Almost always this results in a high probability of a known pathologic diagnosis. Occasionally, clustering falls so far from any known paradigm that a new nosological entity is needed. If so, a new diagnostic label is proposed and possibly endorsed by the medical community, thus entering the “morphology” 5-digit entities of the World Health Organization (WHO) International Classification of Diseases – Oncology (ICD-O) and one of the WHO Classification of Tumours series of books (the WHO “blue books”) [1]. Just as widely known examples in the sarcoma field, liposarcoma, leiomyosarcoma and osteosarcoma are well consolidated entities. The explosion of molecular biology, with the increasing use of massive parallel sequencing, is augmenting our chances to find new clusters and thereby create new potential entities. Probably, few cancers are more exposed thereto than sarcomas. In the last years, in fact, several new entities have been added to the WHO Classification of Tumours—Soft Tissue and Bone Tumours, and many others are legitimate candidates [2]. Thus, in the era of “precision medicine”, sarcomas may be a privileged area to speculate about which requirements are needed for a new cancer entity to exist. All this is not just an academic issue. In fact, how we conceptually cluster diseases in medicine matters a lot about how we approach them therapeutically. Why, amongst cancers, are sarcomas so peculiar? First, they are highly heterogeneous. Only hematological neoplasms do present with so many subgroups. The pathologic heterogeneity of sarcomas was shaped by early pathologists on the basis of morphology. Then, *Correspondence: [email protected] 1 Fondazione IRCCS Istituto Nazionale Tumori, Milano, Italy Full list of author information is available at the end of the article
immunohistochemistry confirmed and widened morphological partitioning. Eventually, molecular biology is doing the same today with morphological and immunohistochemical entities [3]. Possibly more important, only to some extent does sarcoma partitioning correspond to an obvious histogenesis, unlike hematological neoplasms (in which, say, a subgroup of lymphomas may well correspond to a given stage in normal development of lymphocytes). By and large, in fact, liposarcoma, leiomyosarcoma and osteosarcoma correspond to obvious normal tissues, but this is not the case for several other sarcoma entities. Synovial sarcoma, Ewing sarcoma or solitary fibrous tumor are examples thereof. In the most recent WHO Classification of Tumours—Soft Tissue and Bone Tumours, there is a wide array of soft tissue “tumors of uncertain differentiation”, but others can be found amongst the “fibroblastic and myofib
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