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WHO Classification of Tumours
Mucinous adenocarcinoma


Mucinous adenocarcinoma of the breast is characterized by clusters of generally small and uniform cells floating in a lake of extracellular mucin. The mucous lake is compartmentalised by delicate fibrous septae. The cell clusters vary in size and shape and occasionally assume a tubular or, rarely, a papillary arrangement. Atypia, mitoses and microcalcifications are rare. 30-75% of the tumours contain an intraepithelial component with a micropapillary to solid pattern. The tumour usually presents as a palpable mass ranging in size from <1 to >20 cm (average diameter 2.8 cm). Mammography shows a well defined, lobulated lesion.
Pure mucinous carcinomas may be cellular or hypocellular. The cellular variant is more likely to contain intracytoplasmic mucin and argyrophilic granules. When there are other, not mucinous components, the lesion is classified as a mixed tumour. Regular invasive duct carcinoma is the most common admixture.
Mucinous carcinomas are typically estrogen receptor positive, while <70% are progesterone receptor positive.
Only about 2% of breast carcinomas are pure mucinous carcinomas. The tumour affects women over a wide age range (mean age >60 years). In general, the prognosis for pure mucinous carcinoma is favourable, with a 10-year survival of 80-100%. Mixed tumours have a less favourable prognosis. Axillary node metastases occur in 3-15% of pure mucinous carcinomas and in 33-45% of mixed tumours

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Anan K, Mitsuyama S, Tamae K, Nishihara K, Iwashita T, Abe Y, Ihara T, Nakahara S, Katsumoto F, Toyoshima S (2001)
Pathological features of mucinous carcinoma of the breast are favourable for breast-conserving therapy.
Eur J Surg Oncol 27: 459-63

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Toikkanen S, Kujari H (1989)
Pure and mixed mucinous carcinomas of the breast: a clinicopathologic analysis of 61 cases with long-term follow-up.
Hum Pathol 20: 758-64

. Late distant metastases may occur
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Clayton F (1986)
Pure mucinous carcinomas of breast: morphologic features and prognostic correlates.
Hum Pathol 17: 34-8

. In rare cases, cause of death is cerebral infarction as a consequence of mucin embolism to the cerebral arteries
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Towfighi J, Simmonds MA, Davidson EA (1983)
Mucin and fat emboli in mucinous carcinomas. Cause of hemorrhagic cerebral infarcts.
Arch Pathol Lab Med 107: 646-9

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Tavassoli FA, Devilee P (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of the Breast and Female Genital Organs.
3rd Edition
IARC Press: Lyon 2003