A Benign Lesion Similar to Breast Cancer
Breast lesions that mimic malignancies are a significant diagnostic challenge in clinical practice. This case report describes a 60-year-old woman who presented with a painless, inactive small mass in her left breast. The lesion was initially suspected to be breast cancer due to its gross and histological features. However, through detailed pathological examination, immunohistochemistry, and molecular analysis, the lesion was ultimately diagnosed as a radial sclerosing lesion (RSL), a benign entity that closely resembles breast cancer.
The patient had no significant medical history and reported no symptoms other than the presence of the mass. A B-ultrasound revealed a round hypoechoic nodule in the left breast with associated structural distortion. Given the suspicious imaging findings, the patient underwent a lumpectomy, and the excised specimen was subjected to rapid pathological examination using frozen sections.
Macroscopically, the removed breast nodule measured 1.0 cm × 1.0 cm × 0.6 cm. It had a gray-yellow appearance and a hard texture. On the cut surface, the nodule exhibited a dense structure with fine white asterisk-like fibers in the interior and burrs on the edges. The level of the lesion was significantly lower than that of the surrounding breast tissue. A 5-mm thick tissue section was prepared for frozen section examination and stained with hematoxylin and eosin (H&E).
Microscopically, the lesion displayed a radial star-shaped pattern with a central fibrous scar. The mammary ducts within the scar were compressed and surrounded by vigorously proliferating cells. The surrounding glands showed varying degrees of proliferation, arranged radially outward and gradually transitioning into the normal tissue. High-power microscopy revealed the presence of myoepithelial cells surrounding the hyperplastic ductal epithelial cells. The identification of myoepithelial cells was crucial in ruling out malignancy, as their absence is a hallmark of invasive breast cancer. Based on these findings, the lesion was diagnosed as a radial sclerosing lesion (RSL) during the frozen section examination.
The conventional pathology results were consistent with the findings from the frozen section. The lesion exhibited twisted glands and hyperplastic epithelial nests within the hardened fibrous tissue interstitium. Radially arranged mammary ducts and lobules were observed around the lesion. Additionally, apocrine glandular metaplasia and a small amount of calcium deposits were noted in the hyperplastic ductal lumens.
Immunohistochemical analysis was performed to further characterize the lesion. Cytokeratin 5/6 (CK5/6) exhibited a mottled positive expression in the proliferating ductal cells, indicating the presence of basal-like cells. Positive expression of P63 and calponin proteins confirmed the presence of myoepithelial cells, supporting the benign nature of the lesion. To explore the molecular underpinnings of the lesion, phosphatidylinositol-3-kinase (PIK3CA) gene sequencing was performed on 8-mm thick paraffin-embedded tissue sections. No PIK3CA mutations were detected in this case.
The patient was completely cured following the lumpectomy, and the final diagnosis was confirmed as a breast RSL. Radial sclerosing lesions are part of a spectrum of benign sclerotic breast lesions that include radial scars and complex sclerosing adenosis. These lesions are characterized by a central sclerotic area with radially distributed ducts and lobules. Although benign, RSLs can mimic breast cancer both radiologically and histologically, making accurate diagnosis essential.
RSLs are rare but are associated with an increased risk of developing breast cancer. Risk factors include age over 50 years and lesions larger than 4 mm in diameter, particularly those with atypical hyperplasia of ductal epithelial cells. Atypical hyperplasia, especially in the absence of surrounding myoepithelial cells, is a precursor to invasive breast cancer. The presence of myoepithelial cells in this case was a critical factor in distinguishing the lesion from malignancy.
The relationship between RSLs and breast cancer has been explored in several studies. Wilsher et al. reported that RSLs may be neoplastic precursor lesions of low-grade adenosquamous carcinoma (LGASC). They suggested that RSLs and LGASCs form a continuous morphological spectrum, with benign sclerosing lesions at one end and LGASCs at the other. LGASCs are typically more extensive and have a prominent connective tissue stroma.
PIK3CA mutations are commonly found in invasive breast cancers, with a prevalence of 25%–30%. Interestingly, PIK3CA mutations have also been detected in RSLs. Wilsher et al. identified hot spot mutations of PIK3CA in 77% of RSL cases, while Wolters et al. found PIK3CA mutations in 63.6% of RSLs. The remaining cases were wild-type for the screened genes. The absence of PIK3CA mutations in this case highlights the variability in the molecular profile of RSLs and underscores the need for further research to understand their pathogenesis and relationship with breast cancer.
In conclusion, this case report highlights the diagnostic challenges posed by breast lesions that mimic malignancies. Radial sclerosing lesions, though benign, can closely resemble breast cancer in gross and histological features. Accurate diagnosis requires a combination of pathological examination, immunohistochemistry, and molecular analysis. The presence of myoepithelial cells is a key diagnostic feature that helps distinguish RSLs from malignancies. Further studies are needed to elucidate the molecular mechanisms underlying RSLs and their potential role as precursor lesions to breast cancer.
doi.org/10.1097/CM9.0000000000000041
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