Encapsulated papillary carcinoma with invasion in the breast: A case report with imaging findings

Abstract

Encapsulated papillary carcinoma (EPC) of the breast is a rare subtype of papillary carcinoma. EPC with invasion has a higher rate of axillary lymph node metastasis than noninvasive EPC; thus, it is important to assess the presence of invasion using preoperative radiologic imaging. However, there are few comprehensive studies on its imaging characteristics. Herein, we present the case of a 58-year-old woman who noticed a lump in her right breast 2 weeks prior to presentation. Imaging revealed a cystic tumor with solid components, abundant blood flow, and findings suggestive of extracapsular invasion, including a hyperechoic halo on ultrasound and a linear enhancement extending toward the nipple on enhanced MRI. Core needle biopsy diagnosed ductal carcinoma in situ; however, histopathology after total mastectomy confirmed EPC with invasion. The tumor was ER-positive (100%), PgR-positive (60%), and HER2-negative, with a Ki-67 index of 10% and histological grade of 1. The patient underwent axillary lymph node dissection due to macrometastasis, and immediate breast reconstruction with a muscle-preserving deep inferior epigastric perforator (mp-DIEP) flap was performed. Postoperative recovery was uneventful, and she remained recurrence-free on tamoxifen therapy for 2 years. This case highlights key imaging features suggestive of invasion in EPC, which may facilitate preoperative assessment and management.

Introduction

Encapsulated papillary carcinoma (EPC) of the breast, a rare subtype of papillary carcinoma, accounts for approximately 0.5%–2% of all breast malignancies. According to the World Health Organization (WHO), EPC is defined as a low-grade papillary tumor encapsulated by a fibrous capsule lacking myoepithelial cells. On the other hand, EPC with invasion refers to cases in which the tumor extends beyond the capsule, as determined by pathological examination; these tumors with invasion are associated with a higher likelihood of axillary lymph node metastasis. However, imaging findings that indicate extracapsular invasion in EPC remain poorly documented. Herein, we present a case of EPC with invasion in which the invasive component was suspected preoperatively based on imaging findings.

Case presentation

A 58-year-old woman who had not undergone any prior breast cancer screening noticed a lump in her right breast 2 weeks before presentation. She had a history of left breast cancer at age 41, for which she underwent breast-conserving surgery and lymph node biopsy with dissection for a tumor measuring <10 mm; however, the detailed pathological findings were unknown. She also had a history of traumatic brain injury at age 42. Physical examination revealed a mass measuring 25 mm in the inner quadrant of the right breast, with no associated pain, erythema, or nipple discharge.

Digital breast tomosynthesis showed a heterogeneously dense breast composition with a 20 × 17 mm, round, high-density mass with a circumscribed margin in the lower inner quadrant (Fig. 1).

Fig. 1.

Digital breast tomosynthesis revealed a heterogeneously dense breast composition with a 20 × 17 mm, round, high-density mass with a circumscribed margin in the lower inner quadrant of the breast, as seen on the mediolateral oblique view (A) and the craniocaudal view (B).

Ultrasonography revealed a cystic tumor measuring 24 × 22 mm with solid components in the lower inner quadrant (Fig. 2A). A hyperechoic halo at the boundary on the nipple side suggested extracapsular invasion (Fig. 2A). The solid component exhibited abundant blood flow on Doppler imaging (Fig. 2B). A cord-like hypoechoic area extending toward the nipple suggested the presence of an intraductal component (Fig. 2C).

Fig. 2.

Ultrasonography revealed a cystic tumor measuring 24 × 22 mm with solid components in the lower inner quadrant of the breast (A). A hyperechoic halo on the nipple side suggested extracapsular invasion. Doppler imaging revealed abundant blood flow in the solid component (B). A cord-like hypoechoic area extending toward the nipple suggested the presence of an intraductal component (C).

Contrast-enhanced MRI revealed a mass measuring 27 × 20 mm in the lower inner quadrant of the right breast (Fig. 3A and B). The oval-shaped lesion had mixed cystic and solid components (Fig. 3A and B). The solid component exhibited fast and washout enhancement with a heterogeneous pattern, and the apparent diffusion coefficient (ADC) value was 1.20 × 10⁻³ mm²/s. The irregularity of the anterior cranial portion of the capsule suggested extracapsular invasion (Fig. 3C). On the nipple side of the mass, a clumped and linear enhancement was observed, suggesting the presence of an intraductal component (Fig. 3D). There was no evidence of invasion into the pectoral muscle or skin.

Fig. 3.

Contrast-enhanced MRI revealed an oval mass measuring 27 × 20 mm in the lower inner quadrant of the right breast (A and B), with mixed cystic and solid components. The solid portion showed rapid washout enhancement and an ADC value of 1.20 × 10⁻³ mm²/s. Irregularity in the anterior cranial capsule suggested extracapsular invasion (C), while clumped and linear enhancement on the nipple side indicated the presence of an intraductal component (D).

A core needle biopsy diagnosed the lesion as ductal carcinoma in situ (DCIS). Subsequently, the patient underwent a total mastectomy with sentinel lymph node biopsy, which was considered indispensable as clinical assessment and MRI could not reliably exclude invasive carcinoma. This was followed by axillary lymph node dissection due to the presence of macrometastasis. Immediate breast reconstruction with a muscle-preserving deep inferior epigastric perforator (mp-DIEP) flap was performed. The final pathological diagnosis was EPC with invasion, and the invasive component corresponded to the area identified on MRI and ultrasonography (Fig. 4 A–D). The tumor was ER-positive (100%) (Fig. 5A), PgR-positive (60%) (Fig. 5B), and HER2-negative (Fig. 5C). Furthermore, it had a Ki-67 index of 10% (Fig. 5D) with a histological grade of 1, and Elastica–Masson staining revealed venous invasion (Fig. 5E). The tumor capsule showed no cytokeratin staining, indicating the absence of ductal epithelium (Fig. 5F). The intraductal component extending toward the nipple, which was suspected on MRI, was also confirmed pathologically.

Fig. 4.

MRI and US images revealed irregularity in the anterior cranial capsule (A and B), which corresponded to the invasive foci observed in the macroscopic pathological findings (C) and low-magnification histological images (D).

Fig. 5.

The tumor was ER-positive (100%) (A), PgR-positive (60%) (B), and HER2-negative (C). Furthermore, it had a Ki-67 index of 10% (D) with a histological grade of 1. Elastica–Masson staining revealed venous invasion (E), and the tumor capsule showed no cytokeratin staining, indicating the absence of ductal epithelium (F).

The postoperative course was uneventful, and the patient has been on tamoxifen therapy with no signs of recurrence for 2 years.

Discussion

EPC of the breast is a rare subtype of papillary carcinoma, accounting for approximately 0.5%-2% of all breast malignancies [1]. According to the WHO, EPC is commonly observed in postmenopausal women—especially those in their 70s—with a relatively higher occurrence rate in the subareolar region [1,2]. The tumor is defined as a papillary tumor with low-to-moderate nuclear atypia. It is encapsulated by a well-defined fibrous capsule, with limited or no myoepithelial cell staining [3]. In the absence of extracapsular invasion, it is considered a noninvasive cancer with a prognosis similar to that of DCIS [4,5]. Extracapsular invasion is categorized as invasive carcinoma, with the invasive component’s diameter defined as the invasion size. High-grade phenotypes, such as nuclear pleomorphism or increased mitotic activity, are clinically aggressive; therefore, they are appropriately classified as invasive carcinoma [6].

Imaging findings indicating extracapsular invasion in EPC remain poorly documented. There is a paucity of reports focusing specifically on EPC; however, existing studies suggest that certain imaging features may indicate invasion. On mammography, EPC typically presents as a well-circumscribed mass; however, when invasion is present, it may exhibit microlobulated margins or spiculations [7,8]. In a study of 107 cases performed using ultrasound (US), an irregular shape was the only identified predictor of invasion, with no other significant indicators identified [9]. Similarly, in an MRI study of 36 cases, margin irregularity was the sole significant predictor of invasion [10]. These findings highlight the importance of evaluating margin characteristics across imaging modalities when assessing EPC’s invasive potential. In our case, the imaging findings—except for those of mammography—that were predictive of the invasive component are consistent with those reported in the abovementioned reports. In particular, the high signal at the lesion’s boundary on US, known as the halo sign, was clearly visualized and allowed for a reliable diagnosis of invasion. Regarding mammography, digital breast tomosynthesis was also performed; however, no irregular or spiculated margins suggestive of invasion were observed.

Literature is scarce on the relationship between invasion and lymph node involvement in EPC. A study by Ozcan et al. reported lymph node metastasis in only 1 out of 64 EPC cases (1.6%), which was a case of EPC with invasion. Invasion was present in 18 out of 64 EPC cases (28.1%), and among them, lymph node metastasis was observed in 1 out of 18 cases (5.5%) [11]. Furthermore, Solorzano et al. reported that among 40 EPC cases, 13 were invasive (32.5%). These findings suggest that approximately 30% of EPC cases exhibit invasion and that lymph node metastasis tends to be more common in EPC with invasion [12]. Our case was consistent with these findings. In cases of EPC with invasion, the possibility of lymph node metastasis should always be considered in clinical practice.

Conclusion

This case highlights the imaging features of EPC with invasion, demonstrating how extracapsular invasion can be suspected through ultrasonography and MRI. The recognition of these imaging features may aid in the preoperative assessment and management of EPC with invasion.

Patient consent

The patient provided written informed consent for the publication of this case report, including all clinical data and accompanying images.