Mucinous Carcinoma (Colloid Carcinoma) of the Breast

• These tumors are uncommon:

  • In most series account for approximately 2% of invasive breast carcinomas

It is divided into two main subtypes based upon the quantification of cellularity:

• The pure type:

  • In pure mucinous carcinomas:

    • Over 90% of the tumor is made up of malignant cell clusters floating in pools of mucin (see images)

• Frequently, pure mucinous carcinomas can have posterior enhancement by ultrasound imaging:

  • That can lead to mistaking these lesions for cysts

• Patients with pure mucinous carcinomas:

  • Tend to be postmenopausal:

    • Between the ages of 59 and 71 years:

• • • • But it can occasionally occur in patients who are younger than age 40 years:

  • • • • The incidence of mucinous breast cancer in women under 35 years of age is less than 1%

• The mixed type:

• • Tumors in which 50% to 90% of the mass is composed of malignant cell clusters floating in mucin are considered to be a mixed NOS and mucinous category:

  • • Mixed mucinous carcinomas show a less distinct margin, a higher grade, and more mitotically active cytology

  • Their clinicopathologic features:

    • Are similar to those of invasive ductal carcinoma, NOS type

  • Some mucinous breast carcinomas (mainly mixed type) are associated with lobular or ductal neoplasia (in situ or invasive) and some have neuroendocrine differentiation:

    • Mucinous breast carcinoma associated with lobular neoplasia components:

      • Seems to be a biologically distinct subset that frequently shows decreased cell to cell adhesion, loss of cell polarity molecules and lack of neuroendocrine differentiation:

      • • Also in this subset of tumors, the neoplastic cells with signet-ring features are most likely to be found