What question did this study set out to answer?

This report aims to highlight the clinical features and management considerations of invasive mucinous carcinoma in an elderly patient.

March 27, 2026Open Access

Low-Proliferative Invasive Mucinous Carcinoma of the Breast in an Octogenarian: A Case Report Highlighting Pathology-Guided De-escalation

RKRae-Anne KastleKansas City University CAChristopher M AhmadKansas City University RTRachana TadakamallaKansas City University

Key Points

This report aims to highlight the clinical features and management considerations of invasive mucinous carcinoma in an elderly patient.
Case report of an 84-year-old woman with a suspicious breast lesion discovered via routine imaging.
Ultrasound-guided core needle biopsy was performed to confirm the diagnosis of IMC, Grade I/III.
Immunohistochemistry tests were conducted to evaluate hormone receptor status and proliferation index.
The core needle biopsy confirmed invasive mucinous carcinoma involving all sampled cores.
The tumor was characterized by strong estrogen receptor positivity (95%) and progesterone receptor positivity.
The Ki-67 proliferation index was extremely low at approximately 1%, indicating minimal tumor growth.

Abstract

Invasive mucinous carcinoma (IMC) is an uncommon histologic subtype of breast cancer characterized by abundant extracellular mucin and generally indolent behavior. It occurs more frequently in older women and is often associated with favorable prognostic features. An 84-year-old woman with no prior history of breast malignancy was found to have a suspicious lesion in the upper outer quadrant of the left breast on routine imaging. Ultrasound-guided core needle biopsy demonstrated IMC, Grade I/III, involving all four cores, with the largest contiguous tumor focus measuring 1.3 cm. Immunohistochemistry showed strong estrogen receptor positivity (95%), progesterone receptor positivity, human epidermal growth factor receptor 2 negativity (1+), and an extremely low Ki-67 proliferation index (~1%). Pathologic processing met established fixation standards. This case highlights the importance of histologic subtype and proliferative activity in guiding risk stratification and management considerations for breast cancer in elderly patients. Recognition of indolent tumor biology may help avoid overtreatment while maintaining oncologic safety.

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