Squamous metaplasia of lactiferous ducts

Nipple Lesions of the Breast: An Update on Morphologic Features, Immunohistochemical Findings and Differential Diagnosis

Because of the unique anatomic structure of the nipple, a few specific breast lesions occur only at this site. Large lactiferous sinuses may be involved by inflammatory conditions such as squamous metaplasia of lactiferous ducts and ductal ectasia or be the site of uncommon superficial epithelial neoplasms such as nipple adenoma or syringomatous tumor of the nipple. Paget disease of the nipple may be secondary to intraepidermal extension of ductal carcinoma in situ in the underlying lactiferous ducts or develop from malignant transformation of Toker cells. Invasive breast cancer may also arise primarily in the nipple. Most of these conditions present as a palpable mass and/or skin changes with or without nipple discharge. Due to the delicate location and often relatively small size of nipple lesions, biopsy specimens are often superficial and fragmented, and the interpretation is challenging. Knowledge of the morphologic and immunophenotypic features of nipple lesions is essential in making the correct diagnosis. Information on the molecular alterations underpinning nipple neoplasms is currently very limited.

Squamous/epidermoid differentiation in normal breast and salivary gland tissues and their corresponding tumors originate from p63/K5/14-positive progenitor cells

A small group of tumors of breast and salivary glands contains squamous/epidermoid elements as a constitutive feature (e.g., squamous carcinoma, syringomatous tumors, and mucoepidermoid carcinoma). Other tumors (e.g., pleomorphic adenoma, adenomyoepithelial tumors, and adenoid cystic carcinoma) may show occasionally squamous differentiation. Furthermore, squamous metaplasia may be observed in non-neoplastic breast and salivary tissues. However, the histogenesis of these squamous differentiations is far from being understood. Based on our earlier in situ triple immunofluorescence and quantitative reverse transcription (RT)-PCR experiments for basal keratins K5/14 and p63 as well as for glandular keratins (K7/K8/18), squamous keratins (K10 and K13), and myoepithelial lineage markers (smooth muscle actin, SMA), we here traced the squamous/epidermoid differentiation lineage of 60 tumors of the breast and/or salivary glands, cultured tumor cells of 2 tumors, and of 7 squamous metaplasias of non-neoplastic breast and salivary tissues. Our results indicate that both the neoplastic lesions as well as the non-neoplastic squamous metaplasia contain p63/K5/14+ cells that differentiate toward K10/13+ squamous cells. Thus, cells with squamous/epidermoid differentiation undergo a transition from its original p63/K5/14+ precursor state to K10/13+ squamous lineage state, which can be pictured by triple-immunofluorescence experiments. Given the immunophenotypic similarity of p63/K5/14+ tumor cells to their physiological p63/K5/14+ counterparts in normal breast and salivary duct epithelium, we suggest that these cells provide an important histogenetic key to understanding the pathogenesis of squamous differentiation both in normal breast/salivary gland tissues and their corresponding tumors.

Squamous metaplasia of lactiferous ducts (SMOLD)

The aim of this review is to illustrate the mammographic and sonographic appearances of squamous metaplasia of the lactiferous ducts (SMOLD) and to discuss the disease processes of this uncommon breast disease, which shows a strong correlation with smoking. The most common mammographic appearance is of a retro-areolar asymmetrical density. Ultrasonography of the symptomatic breast typically shows a retro-areolar, predominately medial, ill-defined, hypoechoic lesion with either abscess or sinus/fistula formation. Duct dilatation and continuity with lactiferous ducts is commonly seen. Increased vascularity is occasionally seen on colour Doppler ultrasound. Pathology tissue confirmation is always required and this can be by histology of a core biopsy or excision specimen, or fine-needle aspiration (FNA) cytology. Occasionally smears of an associated abundant nipple or sinus discharge may be of value.

Lesions of the Nipple

Because of the singular anatomic structure of the nipple, some breast lesions only occur at this site. The overlying skin includes normal Toker cells near the duct orifices. These cells are occasionally so numerous as to be called Toker cell hyperplasia. Ductal carcinoma in situ (DCIS) may involve nipple skin by direct extension from the underlying ducts (Paget disease of the nipple). The numerous skin appendages (eg, sebaceous, apocrine, and eccrine glands(1)) in the nipple and areola are the likely origin of syringomatous adenomas. At the duct orifices, the normal squamous epithelium dips into the breast for a short distance and abruptly transitions to glandular luminal and myoepithelial cells. When keratin-producing cells extend deeper into the ducts, the condition of squamous metaplasia of lactiferous ducts (SMOLD) results. With age, the lactiferous sinuses are subject to weakened duct walls, inspissated secretions, and rupture, which result in the inflammatory masses or nipple discharge associated with duct ectasia. Superficial epithelial proliferations within the large lactiferous sinuses form nipple adenomas, and deeper proliferations often result in large-duct papillomas. Below the areola is a supporting smooth muscle layer that can give rise to leiomyomas, although these tumors are extraordinarily rare. The proximity of these lesions to the skin results in the majority of them presenting as palpable masses, skin changes, or nipple discharge. Biopsy specimens from these lesions may be small, superficial, or fragmented because of concern about maintaining the cosmetic appearance of the nipple and areola. Knowledge of the location of the biopsy, and the clinical presentation, is often essential in making the correct diagnosis.