Pleomorphic invasive lobular carcinoma of the breast mimicking chronic abscess: a case report

INTRODUCTION

Invasive lobular carcinoma (ILC) accounts for approximately 10–15% of all breast carcinomas and is characterized by loss of E-cadherin, resulting in discohesive tumor cells.^1,2 Pleomorphic invasive lobular carcinoma (PLC) is an uncommon and more aggressive variant, demonstrating marked cytological atypia and a poorer prognosis compared to classical ILC.^3,4 Unlike typical ILC, which is frequently hormone receptor-positive, PLC often exhibits a more variable immunophenotype, including reduced hormone receptor expression and occasional HER2 overexpression.^4,5,6

Additionally, PLC may present with atypical clinical and radiological features, sometimes mimicking benign inflammatory lesions, which can lead to delayed diagnosis and management.^7,8

CASE REPORT

A 36-year-old female presented to the surgical outpatient department at NIMS hospital in Jaipur, Rajasthan, with a history of progressive swelling of the left breast for 2 months. The swelling was insidious in onset and gradually increased in size. It was associated with mild pain and a feeling of heaviness. There was no history of fever, nipple discharge, or trauma. Clinically, the lesion was suspected to represent a chronic breast abscess.

On physical examination, the left breast appeared diffusely enlarged with induration involving almost the entire breast. The overlying skin was stretched but showed no ulceration or peau d’orange appearance. The nipple-areolar complex was distorted. Palpation revealed a poorly defined, firm to hard mass with restricted mobility. Multiple ipsilateral and contralateral axillary lymph nodes were palpable. Ultrasonography of the breast demonstrated an ill-defined, heterogeneous hypoechoic lesion involving the entire left breast parenchyma, extending to the nipple-areolar complex and infiltrating the underlying pectoralis muscle. Minimal internal vascularity was noted on Doppler imaging. Bilateral axillary lymph nodes were enlarged, with the largest measuring 1.8 × 0.9 cm on the left side. The radiological impression favored a malignant etiology, although chronic abscess remained a differential diagnosis.

Fine-needle aspiration cytology (FNAC) from the breast lesion revealed highly cellular smears composed of cohesive clusters and singly dispersed malignant epithelial cells. The cells exhibited a high nucleo–cytoplasmic ratio, marked nuclear pleomorphism, irregular nuclear membranes, coarse chromatin, and prominent nucleoli (Figure 1).

Occasional bizarre tumor cells were also noted. Based on the Yokohama system, the lesion was categorized as malignant (Category V), Robinson grading 2 with a cytological impression suggestive of ductal carcinoma. FNAC from the contralateral axillary lymph node confirmed metastatic carcinoma. The patient subsequently underwent modified radical mastectomy. Gross examination of the specimen revealed a poorly circumscribed, grey-white tumor measuring 8 × 8 × 3.5 cm, involving almost the entire breast. The cut surface was firm with focal areas of necrosis (Figure 2).

Microscopic examination showed tumor cells arranged predominantly in discohesive single-file patterns and loose sheets infiltrating the stroma. The tumor cells exhibited marked pleomorphism, enlarged hyperchromatic nuclei, prominent nucleoli, and moderate eosinophilic cytoplasm (Figure 3). Focal areas showed signet-ring cell morphology and occasional tumor giant cells. Brisk mitotic activity was noted (approximately 10 per 10 high-power fields). Extensive lymphovascular invasion (Figure 3) and perineural invasion were present.

The tumor infiltrated the dermis without overt skin ulceration. Ductal carcinoma in situ, solid pattern without comedo necrosis, intermediate grade was also present (Figure 3). All 22 dissected axillary lymph nodes showed metastatic deposits, many with extranodal extension.

Immunohistochemical analysis demonstrated weak nuclear positivity in 5% of tumour cells for estrogen receptor (ER) (Allred score 1+2=3) (Figure 4) and moderate nuclear intensity in 9% of tumour cells for progesterone receptor (PR) (Allred score 2+2=4) (Figure 4) with strong membranous positivity for HER2 neu (Figure 4), and a Ki proliferative index of 20% (Figure 4). Based on morphological and immunohistochemical findings, a final diagnosis of pleomorphic invasive lobular carcinoma (Nottingham Grade III, pT3N3a), molecular subtype Luminal B subtype with associated Ductal carcinoma in situ without comedo necrosis, intermediate grade was rendered.

DISCUSSION

Pleomorphic invasive lobular carcinoma is a rare but well-recognized variant of lobular carcinoma, first described by Eusebi et al. in 1992.³ Although it shares the classical lobular growth pattern of discohesive cells infiltrating in single-file arrangements, it is distinguished by significant nuclear atypia, prominent nucleoli, and increased mitotic activity.^3,4

In contrast to classical ILC, which is typically ER and PR positive and HER2 negative, PLC demonstrates a more heterogeneous immunoprofile. Several studies have reported reduced hormone receptor expression along with increased HER2 amplification in PLC, contributing to its aggressive biological behavior.^4-6 The HER2-positive and low ER/PR profile observed in the present case supports this aggressive phenotype and has important therapeutic implications, particularly regarding targeted anti-HER2 therapy along with hormone therapy.^8,9 Clinically, PLC tends to present at a more advanced stage with larger tumor size, higher histological grade, and increased incidence of lymph node metastasis.^5,7,10 The extensive lymphovascular invasion and nodal metastasis seen in this case are consistent with previously reported findings and indicate poor prognostic features.^7,10

An unusual aspect of this case was its presentation mimicking a chronic abscess. We report this case to highlight the pitfalls in clinical diagnosis where it was suspected as chronic abscess and cytological misdiagnosis as ductal carcinoma because of the extensive pleomorphism of the epithelial cells; salient point missed in favour of Lobular carcinoma was the cytoplasmic vacuolations. Of significant importance is the cytology of the contralateral axillary lymph node swelling showing dispersed atypical cells with eccentrically placed hyperchromatic nuclei and moderate amount of cytoplasm, which points towards lobular carcinoma. The case was later confirmed in histopathology as Invasive lobular carcinoma, pleomorphic variant. Hence, it is essential to consider the cytomorphological features of the metastatic site as well to avoid misdiagnosis, especially in cytological setting. Two important takeaway lessons from this case report are firstly, expertise and meticulous eye to detail needed while reporting and practicing cytology and secondly, histopathology was, is and will be the gold standard of diagnosis. Malignant breast lesions, especially high-grade tumors, may occasionally present with inflammatory features, leading to diagnostic confusion with benign conditions such as mastitis or abscess.^7,11 This overlap can delay appropriate treatment. Cytologically, PLC may resemble high-grade ductal carcinoma due to marked pleomorphism, making accurate subtyping difficult on FNAC alone.^12,13 Therefore, histopathological examination remains essential for definitive diagnosis. Loss of E-cadherin expression is a key feature supporting lobular differentiation and helps distinguish PLC from ductal carcinoma.^6,14

From a prognostic standpoint, PLC is associated with higher recurrence rates, increased metastatic potential, and reduced overall survival compared to classical ILC.^2,7,13,14 Management generally follows protocols for high-grade breast carcinomas, including surgery, chemotherapy, and targeted therapy. In HER2-positive cases, agents such as trastuzumab significantly improve outcomes.⁹

CONCLUSION

Pleomorphic invasive lobular carcinoma is a rare and aggressive variant of breast carcinoma. Its potential to mimic benign inflammatory lesions poses diagnostic challenges. Early and accurate clinicoradiologic-pathologic correlation is critical to ensure timely management and improved prognostic stratification.

ACKNOWLEDGEMENTS

The authors would like to express gratitude towards Mr. Mohd Adnan (Immunohistochemistry and Histopathology technician) for his support during this case report study.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: Not required

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