*3.11. Sarcomatoid Cells*

Sarcomatoid dedifferentiation is a relatively common finding in high-grade UC. Recent studies have approached the correlation between morphology and genomics in sarcomatoid bladder cancer through analyzing the epithelial to mesenchymal transition process concluding that UC developing sarcomatoid transformation are carcinomas of basal-type [84]. Practically all possible differentiations have been reported in the literature, from undifferentiated spindle cell (Figure 2i) to osteosarcoma. The epithelial component may be scarce or even not identified in some cases, so the diagnosis of primary sarcoma in the urinary bladder should be made with caution in transurethral resection specimens.

An excellent review of this topic based on a MEDLINE database study has been recently published [85].

#### **4. Conclusions**

This narrative collects the varied spectrum of morphological features that can be found in UC. These changes have been organized in architectural and cytological for didactic purposes, but mixtures of them are eventually found in real practice. The goal of this overview is to offer in a few pages the essentials for recognizing them giving diagnostic clues based on morphological and immunohistochemical keys.

**Author Contributions:** C.M. and J.I.L. have designed, reviewed, written, and approved the final version of the manuscript. Both authors have read and agreed to the published version of the manuscript.

**Funding:** José I. López is funded by MINECO, Spain grant ref. SAF2016-79847-R.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **References**


**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
