Holocrine Poroma: A Distinctive Adnexal Tumor

Abstract

There are 36 cases of complex poroid tumors with folliculosebaceous and apocrine differentiation reported in the literature. The authors evaluated 111 poroid tumors including 63 typical eccrine poromas and 48 poroid tumors with folliculosebaceous elements. Folliculosebaceous poroid tumors (FSPT) had basaloid and squamous cells (100%), ducts with steatocystoma-like cuticles and holocrine secretions (89.6%), infundibular follicular structures (66.7%), and entrapped sebocytes (56.3%). No definite apocrine decapitation secretions in FSPT were found. Immunohistochemistry was strongly positive for CK903 and focally positive for CAM5.2, epithelial membrane antigen, and carcinoembryonic antigen. No loss of MLH-1, MSH-2, or MSH-6 mismatch repair proteins was found. FSPT had distinctive features that differentiate them from eccrine poromas including the frequent head and neck locations (62.5% vs. 20.6%, P < 0.01), squamous cytology (100% vs. 1.6%, P < 0.01), more prominent cytoplasmic vacuolization (score 1.4/4.0 vs. 0.3/4.0, P < 0.01), presence of infundibular follicular structures (score 1.2/4.0 vs. 0.03/4.0, P < 0.01), presence of ducts with steatocystoma-like cuticles (89.6% vs. 0.0%, P < 0.01), and less stromal hyalinization (score 1.0/4.0 vs. 2.5/4.0, P < 0.01). The authors propose that FSPT are distinctive benign tumors originating from the sebaceous gland duct and are therefore best categorized as holocrine poroma.

Recurrent PAK2 rearrangements in poroma with folliculo‐sebaceous differentiation

“…identified six poroid tumours with apocrine and sebaceous differentiation and labelled them “infundibular adenoma”. Similar poroid tumours with folliculo‐sebaceous and apocrine differentiation were later reported as “apocrine poroma” or “holocrine poroma” with fewer than 100 published cases 5 . Horenstein et al .…”

“…Similar poroid tumours with folliculosebaceous and apocrine differentiation were later reported as "apocrine poroma" or "holocrine poroma" with fewer than 100 published cases. 5 Horenstein et al published a series of 48 "holocrine poroma" harbouring follicular and sebaceous differentiation. 6 These lesions were more common on the head and neck (62.5%) as shown in our study and in contrast to eccrine poroma, which favour the extremities.…”

“…Tumours with similar morphologic features including follicular, sebaceous, and/or apocrine differentiation were later reported as apocrine/holocrine poroma, referring to the common embryologic origin of all apocrine-folliculosebaceous unit components. [5][6][7] The question as to whether these lesions represent a variant of poroma or a distinct entity is still a matter of debate. 5,7 In this report we describe recurrent PAK2 gene fusion in thirteen cases of poroma with folliculosebaceous differentiation.…”

“…[5][6][7] The question as to whether these lesions represent a variant of poroma or a distinct entity is still a matter of debate. 5,7 In this report we describe recurrent PAK2 gene fusion in thirteen cases of poroma with folliculosebaceous differentiation.…”

“…reported the first description of the “infundibular adenoma”, 4 a tumour with close morphologic similarities with poroma but also harbouring follicular and/or sebaceous differentiation. Tumours with similar morphologic features including follicular, sebaceous, and/or apocrine differentiation were later reported as apocrine/holocrine poroma, referring to the common embryologic origin of all apocrine‐folliculo‐sebaceous unit components 5–7 . The question as to whether these lesions represent a variant of poroma or a distinct entity is still a matter of debate 5,7 …”