Intracholecystic papillary neoplasms of the gallbladder (ICPN) and intraductal papillary neoplasms of the bile duct (IPNB) are characterized by luminal papillary or polypoid neoplastic growth. The neoplastic cells also exhibit downward intramural growths in the forms of intraepithelial extension into non-neoplastic glands (in-situ glandular involvement) including Rokitansky-Aschoff sinus, and stromal invasion (that is invasive carcinoma). The distinction between these two is a challenging pitfall. This synopsis lists histological features that aid the distinction.
The following histological features are indicative of invasive adenocarcinoma:
Isolated single or cluster of tumor cells in the stroma.
Active desmoplasia associated with atypical glands or epithelial cords.
Small or medium-sized, considerably atypical glands in the smooth muscle bundles.
Perineural invasion or vascular invasion by neoplastic cells or glands.
Neoplastic cells on the serosa.
Features favoring non-invasive lesions with ductal-glandular involvement include the following:
Neoplastic glands among or juxtaposing non-neoplastic glands.
Surface spread of dysplastic cells along the duct.
Coexistence of neoplastic and non-neoplastic epithelia in the same glands.
Yasuni Nakanuma and colleagues in Japan reported in the November issue of Human Pathology, 2022 that by these histological features, non-invasive lesion with ductal-glandular involvement is associated with a favorable post-operative overall survival.
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Key References
Nakanuma, Yasuni et al. “Intraepithelial involvement of non-neoplastic glands in papillary preinvasive neoplasms of the biliary tract: a potential diagnostic pitfall.” Human pathology vol. 131 (2023): 98-107. doi:10.1016/j.humpath.2022.11.001
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