# Primary lipomatous tumor/well-differentiated liposarcoma of the breast with invasion of the pectoralis major muscle: A case report

## TL;DR

This case report describes a rare breast tumor that resembles benign lipomas but is actually a moderately malignant liposarcoma, emphasizing the need for accurate diagnosis through imaging and molecular testing.

## Contribution

The report highlights a rare case of breast ALT/WDLS with pectoralis major invasion and introduces novel imaging features and diagnostic protocols for accurate identification.

## Key findings

- ALT/WDLS in the breast is extremely rare, with fewer than 20 global cases documented.
- MDM2/CPM testing is critical for distinguishing ALT/WDLS from benign lipomas due to its 100% sensitivity and specificity.
- Novel imaging features include heterogeneous fat/soft-tissue density and ill-defined tumor-muscle interface (>50 HU/cm gradient).

## Abstract

Atypical Lipoma/Well Differentiated Liposarcoma (ALT/WDLS) is a moderate malignant soft tissue sarcoma originating from mesenchymal tissue. It is the most common subtype of liposarcoma, typically found in the retroperitoneum and limbs. It is extremely rare in the breast. Due to its mild morphology and polymorphic changes associated with various subtypes, ALT/WDLS can easily be mistaken for other benign breast tumors. Accurate diagnosis requires careful evaluation of different morphological features, molecular genetic changes, and clinical characteristics.

This article reports a case of breast ALT/WDLS in a 68 year old female. Examination indicates a mass in the right chest, with unclear boundaries with adjacent chest wall muscle. Subsequently, surgical treatment was performed, and pathological results confirmed ALT/WDLS.

It is rare for ALT/WDLS to originate from the breast. When dealing with breast adipose tissue masses, it is necessary to carefully distinguish the clinical manifestations of benign lipomas and ALT/WDLS. Although ALT/WDLS is moderately malignant, its imaging and clinical similarities to benign lipomas should not be taken lightly in diagnosis. Pathological evaluation and molecular biology examination of tumors can provide important diagnostic criteria for differentiation.

This report emphasizes the need to differentiate benign lipomas from ALT/WDLS when evaluating breast adipose tissue masses. This case also highlights the importance of early detection and accurate diagnosis, reminding clinicians to remain highly vigilant when facing similar cases and to conduct comprehensive diagnosis and treatment through multidisciplinary evaluation.

•Extremely Rare Presentation: Primary breast ALT/WDLS with pectoralis major invasion, among <20 documented cases globally.•Critical Diagnostic Challenges:Mimics benign lipomas; MDM2/CPM testing (100% sensitivity/specificity) and red flags (age > 50, rapid growth, deep location) are critical.•Novel Imaging Correlations: Heterogeneous fat/soft-tissue density, 2-mm fibrous septa (spoke-wheel), ill-defined tumor-muscle interface (>50 HU/cm gradient).•Evidence-Based Management Protocol:High-risk patients:3-month CT + molecular testing; standard: 6-month CT + annual MDM2/CDK4 for 5 years.•Translational Research Implications:CPM as a diagnostic biomarker; molecular stratification for personalized follow-up.

Extremely Rare Presentation: Primary breast ALT/WDLS with pectoralis major invasion, among <20 documented cases globally.

Critical Diagnostic Challenges:Mimics benign lipomas; MDM2/CPM testing (100% sensitivity/specificity) and red flags (age > 50, rapid growth, deep location) are critical.

Novel Imaging Correlations: Heterogeneous fat/soft-tissue density, 2-mm fibrous septa (spoke-wheel), ill-defined tumor-muscle interface (>50 HU/cm gradient).

Evidence-Based Management Protocol:High-risk patients:3-month CT + molecular testing; standard: 6-month CT + annual MDM2/CDK4 for 5 years.

Translational Research Implications:CPM as a diagnostic biomarker; molecular stratification for personalized follow-up.