Nodular Mucinosis of the Breast: A Case Report With Pathologic, Ultrasonographic, and Clinical Findings and Review of the Literature

The Spectrum of Mucinous Lesions of the Breast

CONTEXT.—

Mucinous lesions of the breast encompass many entities ranging from benign to malignant and nonneoplastic to neoplastic. Lesions discussed under this category are mucocele-like lesion, mucinous carcinoma, mucinous micropapillary carcinoma, solid papillary carcinoma, mucinous cystadenocarcinoma, mucoepidermoid carcinoma, invasive lobular carcinoma with extracellular mucin, mucinous ductal carcinoma in situ, and metastasis.

OBJECTIVE.—

To review clinical, pathologic, and molecular features of mucinous lesions of the breast, their differential diagnoses, and challenging features on core needle biopsies.

DATA SOURCES.—

The existing scientific and clinical literature as of December 2021.

CONCLUSIONS.—

The category of mucinous lesions of the breast is vast and the differential diagnosis can be challenging, especially on core needle biopsies. In all cases, clinical, radiologic, and pathologic correlation is necessary to reach a comprehensive diagnosis. Given that the prognosis and management of each entity is different, being aware of these entities and their nuances is critical for a pathologist to guide accurate management.

A review of mucinous lesions of the breast

Mucinous lesions of the breast include a variety of benign and malignant epithelial processes that display intracytoplasmic or extracellular mucin, including mucocele-like lesions, mucinous carcinoma, solid papillary carcinoma, and other rare subtypes of mucin-producing carcinoma. The finding of free-floating or stromal mucin accumulations is a diagnostic challenge of which the significance depends on the clinical, radiologic, and pathologic context. This article emphasizes the differential diagnosis between benign and malignant mucin-producing lesions, with a brief consideration of potential mimics, such as biphasic and mesenchymal lesions with associated with mucinous, myxoid, or matrix material.

[Nodular mucinosis of the breast]

Nodular mucinosis of the breast is a rare entity of uncertain histogenesis and with benign behavior. It usually presents as an asymptomatic tumor around the nipple or areola and located in the dermis or subcutaneous cellular tissue. We present a case of typical nodular mucinosis. Histologically it is defined as being composed of irregular lakes of mucin negative with PAS but positive with colloidal iron and alcian blue. Mucin is accompanied by fibrous stroma with a scarce component of fusiform cells. Some authors suggest a possible myofibroblastic origin. However, molecular studies of nodular mucinosis have not been performed. The differential diagnosis must be made mainly with benign and malignant mammary lesions of mucinous stroma. In the literature, 13 cases of nodular mucinosis are described.

Mesenchymal Lesions of the Breast: What Radiologists Need to Know

OBJECTIVE

Mesenchymal breast tumors originate from the various components of mammary stroma. The aim of this review is to discuss the clinical presentation, imaging appearance, and management of mesenchymal breast lesions.

CONCLUSION

Although many mesenchymal tumors exhibit characteristic findings on imaging, others show nonspecific characteristics and require tissue biopsy for diagnosis. An awareness of the clinical and imaging presentation is essential in guiding the differential diagnosis and patient management.

Benign Fibromyxoid Lesion of the Breast: A Distinct Entity From Benign Spindle Cell Tumors of the Mammary Stroma?

Myxoid lesions of the breast can be diagnostically challenging entities. We report 4 cases of CD34+ fibromyxoid lesion that have been previously diagnosed as “benign myxoid lesion,” “nodular mucinosis,” or “mammary myofibroblastoma, myxoid type” on the basis of CD34-positivity. The lesions were microscopically well circumscribed and composed of a paucicellular spindle cell proliferation in a background of myxoid stroma. No epithelial component was identified. The spindle cells showed immunohistochemical reactivity for CD34 and smooth muscle actin. Based on morphologic and immunohistochemical similarities between these cases and myxoid myofibroblastoma, we compared 4 myxoid lesions with cases of typical myofibroblastoma, utilizing retinoblastoma (Rb) antibody and fluorescent in situ hybridization for 13q14 gene rearrangement (encoding the Rb gene). The myxoid lesions showed retention of Rb protein by immunohistochemistry, whereas Rb expression was lost in cases of myofibroblastoma. We identified loss of 13q14 in 3 of 4 cases of myofibroblastoma. Notably, 13q14 gene rearrangement was not observed in any of the myxoid lesions. Our data show that there is at least a subset of CD34+ fibromyxoid lesions that, despite overlapping morphologic and immunohistochemical phenotype and proposed common histogenesis with myofibroblastomas, is genetically distinct from the latter based on Rb analysis.

An Update of Mucinous Lesions of the Breast

Mucinous lesions of the breast include a variety of benign and malignant epithelial processes that display intracytoplasmic or extracellular mucin, including mucocelelike lesions, mucinous carcinoma, solid papillary carcinoma, and other rare subtypes of mucin-producing carcinoma. The most important diagnostic challenge is the finding of free-floating or stromal mucin accumulations for which the significance depends on the clinical, radiologic, and pathologic context. This article emphasizes the differential diagnosis between mucocelelike lesions and mucinous carcinoma, with a brief consideration of potential mimics, such as biphasic and mesenchymal lesions with myxoid stroma ("stromal mucin") and foreign material.

Fine-needle aspiration of superficial myxoid neurofibroma in the region of the breast

Myxoid neurofibromas are benign spindle cell tumors of perineural cell origin with a broad pathologic differential diagnosis, which includes myxoma, myxoid liposarcoma, myxoid dermatofibrosarcoma protuberans, and low-grade fibromyxoid sarcoma. We present an unusual case of superficial myxoid neurofibroma in the region of the breast that underwent pre-operative fine-needle aspiration (FNA). The differential diagnosis for a myxoid subcutaneous lesion should include myxoid neurofibroma when myxoid material is encountered in an otherwise hypocellular FNA.

Papular mucinosis of the breast after radiation therapy

Localized papular mucinosis is a type of mucinosis induced by several different causes. However, to the best of our knowledge, prior radiation therapy has not been reported to be related to papular mucinosis. We present a case of a 47-year-old woman who had undergone an operation for a breast carcinoma 2 years earlier and received local radiotherapy in the affected breast. Currently, she presents multiple erythematous papules that are caused by abundant dermal mucin deposits. We discuss some potential differential diagnoses.

Nodular Mucinosis of the Breast in a Male: Reassessment of Diagnostic Criteria and Proposal for Its Classification as a Soft Tissue Tumor in the Myofibroblastoma and Spindle Cell Lipoma Spectrum

Nodular mucinosis of the breast (NMB) is a rare entity with only a few cases described in the literature, most of them in young girls. All cases are located in the nipple and areolar area and microscopically consist of a multinodular myxoid mesenchymal proliferation. Bands of sclerotic collagen containing preexisting breast ducts and abundant vascularization are other features typical of NMB. No relation to Carney complex has been reported, and an indolent behavior is the rule in all patients. We present a case of NMB occurring in the nipple of a 46-year-old man and analyze the clinicopathological features of the other cases of NMB reported in the English literature, concluding that two of them most likely correspond to trauma-induced cutaneous focal mucinosis of the mammary areola. Finally, we review diagnostic criteria for NMB and elaborate an ontogenetic hypothesis based on both its morphological resemblance to myofibroblastoma and its immunohistochemical profile.

Mucinous Lesions of the Breast

Breast lesions associated with extracellular mucin production are uncommon and constitute a wide spectrum of lesions ranging from benign cyst to mucinous carcinoma. Intracytoplasmic mucin can be seen rarely in benign metaplasias but is a common finding in invasive and in situ carcinomas. In this article, we discuss the differential diagnosis of breast lesions associated with mucin production and other entities that show histologic changes that mimic mucin production.