Value of Multimodality Imaging in Diagnosing Primary Small Cell Carcinoma of Breast
Primary small cell carcinoma of the breast (PSCCB) is an exceedingly rare and aggressive form of invasive breast cancer with neuroendocrine features. Its pathogenesis remains largely unknown, though some researchers suggest it may originate from multipotent stem cells that have developed neuroendocrine characteristics. PSCCB accounts for less than 1% of all primary breast cancers, with a mean age of onset at 53 years, ranging from 28 to 81 years. Clinically, PSCCB often presents as a palpable breast mass discovered incidentally during a physical examination, as it lacks distinctive symptoms such as skin redness or nipple discharge. Due to its rarity and atypical presentation, PSCCB poses significant diagnostic and therapeutic challenges. This article explores the value of multimodality imaging in diagnosing PSCCB, based on a detailed case study of a 51-year-old woman, and discusses the implications for treatment and prognosis.
Clinical Presentation and Initial Imaging Findings
The patient, a 51-year-old woman, presented with a palpable mass in the lower outer region of her left breast. There was no history of skin redness, nipple discharge, or other associated symptoms. Initial diagnostic imaging included mammography, ultrasonography (US), and magnetic resonance imaging (MRI), each providing critical insights into the nature of the lesion.
Mammography revealed a circular, homogenous mass with well-defined margins and no evidence of calcification, located in the posterior region of the left breast. This finding, while indicative of a mass, was nonspecific and did not immediately suggest malignancy.
Ultrasonography provided further details, demonstrating a heterogeneous, hypoechoic lesion with peripheral blood flow signals. The resistance index (RI) was measured at 0.6, and the elastic score was 4.0, both of which raised suspicion for malignancy. The hypoechoic nature of the lesion and the presence of blood flow are often associated with aggressive tumors, prompting further investigation.
Magnetic Resonance Imaging (MRI) was subsequently performed, revealing a mass measuring approximately 2.6 cm × 2.5 cm. On T1-weighted images, the lesion exhibited decreased signal intensity, while fat-suppressed T2-weighted images showed an area of very high signal intensity. Diffusion-weighted imaging (DWI) revealed a high signal within the lesion, and the apparent diffusion coefficient (ADC) value was calculated at 0.893 × 10⁻³ mm²/s, which is relatively low and suggestive of malignancy. Contrast-enhanced T1-weighted fat-saturated images displayed heterogeneous rim enhancement, and the time-intensity curve exhibited a plateau pattern, further supporting the suspicion of a malignant lesion.
Pathologic Confirmation and Advanced Imaging
Given the concerning imaging findings, the patient underwent an ultrasound-guided core-needle biopsy of the left breast mass. Pathologic evaluation confirmed the diagnosis of small cell carcinoma (SCC). Immunohistochemical analysis revealed that the tumor cells were negative for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). However, the Ki-67 proliferation index was greater than 90%, indicating a highly proliferative tumor. Additionally, the tumor cells were positive for neuroendocrine differentiation markers, including synaptophysin, chromogranin A, neuron-specific enolase, and CD56, confirming the diagnosis of PSCCB.
To rule out the possibility of metastasis from another primary site, a fluorine 18 fluorodeoxyglucose integrated positron emission tomography and computed tomography (18FDG PET-CT) scan was performed. The scan showed accumulation of the radiotracer in the left breast lesion but no evidence of extramammary accumulation, confirming the primary nature of the breast tumor.
Surgical Intervention and Postoperative Findings
Based on the imaging findings and pathologic diagnosis, the patient underwent surgery, which included local expansion of the left breast cancer resection and left axillary sentinel lymph node biopsy. Postoperative pathology revealed infiltrating nests of small cells within the fibrotic stroma. The tumor cells exhibited hyperchromatic nuclei, scant cytoplasm, and small areas of necrosis at the tumor edges, consistent with the characteristics of small cell carcinoma.
Imaging Characteristics of PSCCB
The imaging features of PSCCB are not well-documented due to its rarity. However, based on this case and previous reports, PSCCB can exhibit a range of imaging findings depending on the proportion of small cell carcinoma (SCC) and ductal carcinoma in situ (DCIS) components within the tumor. When DCIS predominates, the imaging findings may resemble those of DCIS, such as calcifications and architectural distortions. Conversely, when SCC is the dominant component, the tumor tends to exhibit features of high-grade malignancy, including rapid growth, central necrosis, and a “scar-like” appearance.
In this case, the multimodality imaging findings were consistent with those of triple-negative breast cancer (TNBC), including a mass with well-defined margins, high intratumoral signal intensity on T2-weighted images, low ADC values, heterogeneous rim enhancement, and a plateau or washout pattern on contrast-enhanced MRI. These findings suggest that the pathologic components of PSCCB in this case were predominantly SCC, with DCIS playing a secondary role.
Differential Diagnosis
PSCCB must be differentiated from other mammary epithelial tumors based on their imaging and pathologic characteristics. For example, mucinous carcinoma often presents with persistent enhancement patterns and very high ADC values, which can help distinguish it from PSCCB. Medullary carcinoma, another differential diagnosis, is characterized by well-circumscribed tumors with central necrosis and prominent lymphoid infiltration, which can overlap with the imaging features of PSCCB. Pathologic biopsy remains the gold standard for definitive diagnosis, particularly in distinguishing PSCCB from other small cell carcinomas that may metastasize to the breast.
Treatment and Prognosis
Due to the rarity of PSCCB, there are no established treatment guidelines or consensus. Management strategies are often extrapolated from guidelines for invasive breast cancer and small cell lung cancer. In this case, the patient underwent surgical resection followed by adjuvant chemotherapy consisting of four cycles of etoposide and cisplatin. The choice of treatment was influenced by the aggressive nature of the tumor and its similarity to TNBC, which is typically managed with surgery, chemotherapy, and radiotherapy.
Prognostic data for PSCCB are limited, but retrospective studies suggest a mortality rate of approximately 18.9% with a mean follow-up of 20.75 months. Early recognition and aggressive treatment are crucial for improving outcomes. Multimodality imaging plays a vital role in pretreatment planning, prognosis prediction, and enhancing the understanding of the biologic behavior of PSCCB.
Conclusion
Primary small cell carcinoma of the breast is a rare and aggressive malignancy with neuroendocrine features. Multimodality imaging, including mammography, ultrasonography, MRI, and PET-CT, is essential for accurate diagnosis, staging, and treatment planning. In this case, the imaging findings were consistent with those of triple-negative breast cancer, highlighting the importance of integrating imaging and pathologic data for definitive diagnosis. Early recognition and aggressive treatment, including surgery and adjuvant chemotherapy, are critical for improving patient outcomes. Further research and case reports are needed to better understand the imaging characteristics, biologic behavior, and optimal management strategies for PSCCB.
doi.org/10.1097/CM9.0000000000000226
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