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INDIANA ASSOCIATION OF PATHOLOGISTS


April 2019

FINAL DIAGNOSIS AND DISCUSSION

Final diagnosis: Micropapillary urothelial carcinoma.

Discussion: Micropapillary urothelial carcinoma (MPUC) of urinary bladder is a rare variant of urothelial carcinoma with a histologic appearance similar to micropapillary carcinoma arising in the ovary, lung, breast, or other anatomic locations [1, 2].

MPUC is often at an advanced stage at the time of diagnosis. It displays aggressive clinical characteristics, responds poorly to intravesical therapy, and shows a higher mortality than conventional urothelial carcinoma.

The morphological characteristic features of MPUC include: 1) multiple nests in the same lacunar space; 2) intracytoplasmic vacuolization; 3) epithelial ring formation in the papillae; and 4) is frequently admixed with conventional urothelial carcinoma or other variant histology [3].

When considering the differential diagnosis, the MPUC should be distinguished from conventional invasive urothelial carcinoma with extensive stromal retraction. Stromal retraction is relatively common in conventional invasive urothelial carcinoma and the morphologic difference between MPUC and conventional urothelial carcinoma can be very challenging. It has been shown that predominantly medium-sized tumor nests and nest anastomosis or branching are features of conventional urothelial carcinoma. Metastatic micropapillary adenocarcinoma of lung, breast, and ovary should also be ruled out because these tumors are morphologically identical to micropapillary urothelial carcinoma. Clinical and radiological correlation and immunohistochemistry are very useful in determining a primary tumor in most situations.

References:

1. Lopez-Beltran A, Henriques V, Montironi R, Cimadamore A, Raspollini MR, Cheng L. Variants and new entities of bladder cancer. Histopathology 2019; 74, 77-96.

2. Cheng L, MacLennan GT, Bostwick DG. Urologic Surgical Pathology, Fourth edition, Elsevier, Philadelphia, PA, 2019.

3. Sangoi AR, Beck AH, Amin MB, Cheng L, Epstein JI, Hansel DE, Iczkowski KA, Lopez-Beltran A, Oliva E, Paner GP, Reuter VE, Ro JY, Shah RB, Shen SS, Tamboli P, McKenney JK. Interobserver reproducibility in the diagnosis of invasive micropapillary carcinoma of the urinary tract among urologic pathologists. Am J Surg Pathol 2010; 34, 1367-1376.


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