Microcystic Variant of Urothelial Carcinoma: A Review and Update

Background: Microcystic variant of urothelial carcinoma is one of the new variants of urothelial carcinoma that was added to the WHO classification in 2004.

Aims: To review the literature on microcystic variant of urothelial carcinoma.

Materials and Methods: Various internet search engines were used to document the presentation, diagnosis, management and outcomes of microcystic variant of urothelial carcinoma.

Results: (Summary of the Review and Update of the Literature): Microcystic urothelial carcinoma is a rare variant of urothelial carcinoma which was added to the WHO classification in 2004.

Microscopic examination of microcystic variant of urothelial carcinoma tends to reveal the ensuing characteristic features:

Conspicuous intracellular and intercellular lumina / microcysts encompassed by malignant urothelial or squamous cells.
The lumina tend to be empty but they may contain granular eosinophilic debris, mucin, or necrotic cells.
The cysts tend to be variable in size and they are either round or oval, up to 2mm; they are lined by urothelium which are either flattened cells or low columnar cells however, they do not contain colonic epithelium or goblet cells.
The cysts tend to be infiltrative and they may invade the muscularis propria.
Their microscopic pattern mimics cystitis cystica and cystitis glandularis which should be considered as differential diagnoses.
Elongated and irregular branching spaces are usually seen.
Occasionally they may exhibit neuroendocrine differentiation.
Out of about 17 cases of microcystic variant of urothelial carcinoma that had earlier on been reported, only 2 patients had survived. Three more patients were reported from 2017 to 2020 and two of them had survived for 2 years in one case, six months in another case, but definite confirmation of the outcome of the third person as to how long he survived was not available to the author.

Because of the rarity of microcystic variant of urothelial carcinoma its biological behaviour is not well known but there is some evidence to suggest that this tumour tends to be of high-grade and high-stage. There is also no consensus opinion on the best option of treatment of the tumour.

Conclusions: Microcystic variant of urothelial carcinoma is a rare tumour and to the knowledge of the author less than 25 cases have been reported in the literature.

In view of the limited number of reported cases of microcystic variant of urothelial carcinoma in the literature, it would prove difficult at the moment to be dogmatic regarding its prognosis.

However, it would appear from the few reported cases of microcystic urothelial carcinoma that on the whole this tumour is a highly aggressive tumour.

Urologists, pathologists and oncologists throughout the world should be encouraged to report new cases of microcystic urothelial carcinoma in order to document the biological behaviour such a rare tumour.