Nested variant of urothelial carcinoma

Abstract

Background. Nested variant of urothelial carcinoma was added to the WHO's classification in 2004. Aims. To review the literature on nested variant of urothelial carcinoma. Results. About 200 cases of the tumour have been reported so far and it has the ensuing morphological features: large numbers of small confluent irregular nests of bland-appearing, closely packed, haphazardly arranged, and poorly defined urothelial cells infiltrating the lamina propria and the muscularis propria. The tumour has a bland histomorphologic appearance, has an aggressive biological behaviour, and has at times been misdiagnosed as a benign lesion which had led to a significant delay in the establishment of the correct diagnosis and contributing to the advanced stage of the disease. Immunohistochemically, the tumour shares some characteristic features with high-risk conventional urothelial carcinomas such as high proliferation index and loss of p27 expression. However, p53, bcl-2, or EGF-r immunoreactivity is not frequently seen. The tumour must be differentiated from a number of proliferative lesions of the urothelium. Conclusions. Correct and early diagnosis of this tumour is essential to provide early curative treatment to avoid diagnosis at an advanced stage. A multicentre trial is required to identify treatment options that would improve the outcome of this tumour.

Figure 1

Low-power view showing closely packed, irregularly spaced, glandular, and cystic urothelial nests somewhat resembling von Brunn nests. Note that the overlying urothelium appears uninvolved (hematoxylin-eosin, original magnification ×100). Nested variant of urothelial carcinoma taken from Dhall et al. [2]. The figures have been reproduced with the permission of the editor in chief of Archives of Pathology and Laboratory Medicine on behalf of the editorial board of the journal.

Figure 2

Low-power view showing bland tumor cells in the nested pattern infiltrating the muscularis propria (hematoxylin-eosin, original magnification ×100). Nested variant of urothelial carcinoma taken from Dhall et al. [2]. The figures have been reproduced with the permission of the editor in chief of Archives of Pathology and Laboratory Medicine on behalf of the editorial board of the journal.

Figure 3

On high-power view, the tumour cells show no significant cytologic atypia (hematoxylin-eosin, original magnification ×400). Nested variant of urothelial carcinoma taken from Dhall et al. [2]. The figures have been reproduced with the permission of the editor in chief of Archives of Pathology and Laboratory Medicine on behalf of the editorial board of the journal.

Figure 4

von Brunn nests in comparison with nested variant of urothelial carcinoma showing regularly spaced urothelial nests with a relatively flat base (hematoxylin-eosin, original magnification ×200). Nested variant of urothelial carcinoma taken from Dhall et al. [2]. The figures have been reproduced with the permission of the editor in chief of Archives of Pathology and Laboratory Medicine on behalf of the editorial board of the journal.

Figure 5

Gross photo of Case  1 shows an edematous urinary bladder mucosa and markedly and diffusely thickened bladder wall Xiao et al. [28].

Figure 6

The neoplastic cells form ill-defined nests with a diffuse growth pattern. Some tumor cells have clear cytoplasm. The surface mucosa is not involved by the underlying tumor (Case  1) (hematoxylin-eosin, original magnification ×200) Xiao et al. [28].

Figure 7

The nuclei of the tumor cells are relatively uniform with finely granular chromatin, inconspicuous nucleoli, and rare mitosis (Case  1) (hematoxylin-eosin, original magnification ×400) Xiao et al. [28].

Figure 8

The neoplastic cells are strongly immunoreactive for p63 (Case  1) (p63, original magnification ×200) Xiao et al. [28].

Figure 9

The cytologically bland neoplastic cells are arranged in a diffuse pattern of relatively ill-defined and variably sized nests (Case  2) (hematoxylin-eosin, original magnification ×600) Xiao et al. [28].

Figure 10

The neoplastic cells are strongly immunoreactive for p63 (Case  2) (p63, original magnification ×400) Xiao et al. [28].