|
Adenoid basal carcinoma (ABC) is a rare tumor of the cervix, with the incidence about 1-2% of cervical cancers [1]. It usually affects postmenopausal women. Patients are typically asymptomatic and the tumor is discovered as an incidental finding. Microscopically, it is composed of variably sized nests of cells that show infiltrative growth pattern without associated desmoplastic stroma. The tumor nests typically show peripheral palisading, and may be solid or have central lumina filled with necrotic debris. The tumor cells display bland cytonuclear features with uniform, round to oval basophilic nuclei without nucleoli or mitoses. Occasionally cells may show clear cell changes. The term “adenoid basal hyperplasia (ABH)” has been described as a proliferation of small basaloid nests that extends less than 1 mm from the basement membrane [2].
ABCs are thought to originate from the reserve cervical cells, and are often associated (>90% of cases) with high-grade squamous intraepithelial lesion. P53 alteration and HPV type 16 appear to play significant roles in the pathogenesis of these lesions [3,4]. Immunohistochemical stains show that the tumor cells are positive for p16 (diffuse expression), p63, CAM5.2, EMA, CK7 and CEA [5]. ABC can be also associated with other conventional cervical malignancies, such as adenoid cystic carcinoma, squamous cell carcinoma, small cell neuroendocrine and adenosquamous carcinoma, and these cases should be reported as “mixed carcinoma” [4,6].
The differential diagnosis of ABC includes adenoid cystic carcinoma, basaloid squamous cell carcinoma and neuroendocrine tumors. Adenoid cystic carcinoma is usually a mass forming lesion, and histologically shows a prominent cribriform growth pattern with extracellular basement membrane-like material and associated desmoplastic stroma. Cytologically, the tumor cells show enlarged hyperchromatic nuclei and brisk mitotic activity. Immunohistochemically, the tumor is positive for CD117, while ABCs are usually negative or equivocal.
Basaloid squamous cell carcinoma, a variant of squamous cell carcinoma, shows nests of small cells with lack of maturation, minimal keratinization, high-grade nuclei, increased mitoses and associated necrosis. As noted, ABC sometimes can show foci of squamous metaplasia, and such metaplasia may be so extensive and may contain cells showing atypia, which can cause the lesion to simulate an invasive squamous cell carcinoma.
Neuroendocrine tumors usually show insular, trabecular, glandular or solid growth pattern. The tumor nests show no peripheral palisading. Cytologically, the tumor cells of low-grade neuroendocrine tumors show abundant, finely granular cytoplasm, round to oval nuclei with stippled (salt and pepper) chromatin and conspicuous nucleoli. In contrast, high-grade neuroendocrine carcinomas are characterized by nuclear hyperchromasia and abundant mitotic and apoptotic activity. For difficult cases, an immunohistochemical panel including neuroendocrine markers may be useful.
It is important to differentiate ABCs from other lesions, given that clinically, pure lesions have a largely indolent nature, and do not show tumor recurrence, metastases or tumor-associated death, irrespective of the modality of treatment. The outcome of mixed carcinomas is predominantly dependent on the non-ABC component.
References
1. Michael J Russell, Oluwole Fadare. Adenoid basal lesions of the uterine cervix: evolving terminology and clinicopathological concepts. Diagn Pathol. 2006; 1: 18.
2. Brainard JA, Hart WR. Adenoid basal epitheliomas of the uterine cervix: a reevaluation of distinctive cervical basaloid lesions currently classified as adenoid basal carcinoma and adenoid basal hyperplasia. Am J Surg Pathol. 1998;22:965–75.
3. Goyal A, Wang Z, Przybycin CG, Yang B. Application of p16 Immunohistochemistry and RNA In Situ Hybridization in the Classification of Adenoid Basal Tumors of the Cervix. Int J Gynecol Pathol. 2016 Jan;35(1):82-91.
4. Anil V. Parwani, Ann E. Smith Sehdev, Robert J. Kurman, Brigitte M. Ronnett. Cervical adenoid basal tumors comprised of adenoid basal epithelioma associated with various types of invasive carcinoma: clinicopathologic features, human papillomavirus DNA detection, and P16 expression. Hum Pathol. 2005 Jan; 36(1): 82–90.
5. Senzaki H, Osaki T, Uemura Y, Kiyozuka Y, Oqura E, Okamura A, Tsubura A. Adenoid basal carcinoma of the uterine cervix: immunohistochemical study and literature review. Jpn J Clin Oncol. 1997 Dec;27(6): 437-41.
6. Priya Pathak, Nadeem Tanveer. Adenoid Basal Carcinoma of the Uterine Cervix in Association with Keratinizing Squamous Cell Carcinoma: a Rare Diagnosis. Indian J Surg Oncol. 2019 Sep; 10(3): 451–453.