CYLD-mutant cylindroma-like basaloid carcinoma of the anus: a genetically and morphologically distinct class of HPV-related anal carcinoma

Abstract

Rare reports of anal carcinoma (AC) describe histologic resemblance to cutaneous cylindroma, but mutations in the tumor suppressor CYLD, the gene responsible for familial and sporadic cylindromas, have not been systematically investigated in AC. Here, we investigate CYLD-mutant AC, focusing on molecular correlates of distinct histopathology. Comprehensive genomic profiling (hybrid-capture-based DNA sequencing) was performed on 574 ACs, of which 75 unique cases (13%) harbored a CYLD mutation. Clinical data, pathology reports, and histopathology were reviewed for each CYLD-mutant case. The spectrum of CYLD mutations included truncating (n = 50; 67%), homozygous deletion (n = 10; 13%), missense (n = 16; 21%), and splice-site (n = 3; 4%) events. Compared with CYLD-wildtype AC (n = 499), CYLD-mutant ACs were significantly enriched for females (88% vs. 67%, p = 0.0001), slightly younger (median age 59 vs. 61 years, p = 0.047), and included near-universal detection of high-risk HPV sequences (97% vs. 88%, p = 0.014), predominantly HPV16 (96%). The CYLD-mutant cohort also showed significantly lower tumor mutational burden (TMB; median 2.6 vs. 5.2 mut/Mb, p < 0.00001) and less frequent alterations in PIK3CA (13% vs. 31%, p = 0.0015). On histopathologic examination, 73% of CYLD-mutant AC (55/75 cases) showed a striking cylindroma-like histomorphology, composed of aggregates of basaloid cells surrounded by thickened basement membranes and containing characteristic hyaline globules, while only 8% of CYLD-wildtype tumors (n = 34/409) contained cylindroma-like hyaline globules (p < 0.0001). CYLD-mutant carcinomas with cylindroma-like histomorphology (n = 55) showed significantly lower TMB compared with CYLD-mutant cases showing basaloid histology without the distinctive hyaline globules (n = 14) (median 1.7 vs. 4.4 mut/Mb, p = 0.0058). Only five CYLD-mutant cases (7%) showed nonbasaloid conventional squamous cell carcinoma histology (median TMB = 5.2 mut/Mb), and a single CYLD-mutant case showed transitional cell carcinoma-like histology. Within our cohort of ACs, CYLD mutations characterize a surprisingly large subset (13%), with distinct clinical and genomic features and, predominantly, a striking cylindroma-like histopathology, representing a genotype-phenotype correlation which may assist in classification of AC.

Fig. 1. Anal carcinomas with CYLD mutation and cylindroma-like histopathologic features.

a Histopathologic examination reveals a carcinoma involving the dermis composed of rounded lobules of basaloid cells with hyaline inclusions and focally thickened basement membrane (H&E, 100×). b Higher power examination of this tumor reveals foci of necrosis and hyaline globules (H&E, 200×). c Carcinoma with hyaline globules and associated thickened basement membrane (H&E 400×) d Carcinoma with prominent jigsaw-like arrangement of basaloid cells with peripheral palisading, surrounding thickened basement membrane, and small hyaline globules (H&E, 200×). e, f This metastatic carcinoma involving the lung is composed of irregular lobules of basaloid cells with central necrosis and focal basement membrane inclusions (H&E, 100×, and 400×). g Carcinoma with pleomorphic basaloid cells with focal hyaline globules (H&E, 200×) (h) Carcinoma with thickened basement membrane and hyaline globules, also showing biphasic admixture of basaloid cells and cells with paler nuclei (H&E, 200×).

Fig. 2. Anal carcinomas with CYLD mutation lacking cylindroma-like basement membrane inclusions.

(a and inset) Anal carcinoma composed predominantly of irregular aggregates of basaloid cells showing rare continuity with surface epithelium (a) and focal squamous eddies (inset) (H&E, 200×). b Metastatic anal basaloid carcinoma involving a lymph node with infiltrative small aggregates of basaloid cells with occasional squamous morules (H&E 200×). c Basaloid anal carcinoma, metastatic to liver, consisting of large aggregates of basaloid tumor cells without apparent basement membrane material or squamous differentiation (H&E, 100×). d Basaloid anal carcinoma with small, closely apposed aggregates of basaloid tumor cells without apparent basement membrane inclusions or squamous differentiation (H&E, 200×). e Anal carcinoma composed of aggregates of cells with glassy eosinophilic cytoplasm, consistent with conventional squamous cell carcinoma (H&E, 100×). f A single case showed thickened trabeculae of basaloid carcinoma cells with a transitional cell carcinoma-like appearance (H&E, 100×).

Fig. 3. Clinicopathologic features and molecular landscape of CYLD-mutant anal carcinoma.

a Tile plot to summarize clinical features, histopathology, and molecular alterations in CYLD-mutant anal carcinoma. b Schematic of functional domains of CYLD (transcript NM_015247), to include identified mutation sites (79 mutations in 75 cases). The resulting terminal amino acid location for nonsense (n = 38) and frameshift mutations (n = 12) in CYLD are denoted by black and orange bars, respectively (top of diagram). Missense mutations (n = 16) and splice site mutations (n = 3), each identified in single case, are labeled with black and orange arrows, respectively (lower diagram). Mutations in gray font were identified in cases with conventional squamous cell carcinoma histology. Ten cases with homozygous deletions in CYLD are not shown in (b). CAP cytoskeleton-associated proteins, P phosphorylation region.