Case report: Carcinoma en cuirasse-widespread cutaneous metastases from breast adenocarcinoma.

[RATIONALE] Cutaneous metastatic carcinoma is a malignant tumor that originates outside the skin. Studies have found that the most common primary tumor in female patients with cutaneous metastatic carcinoma is breast cancer. Cutaneous metastatic carcinoma spreads to the adjacent skin through blood vessels, lymphatics, or interstitial spaces. It forms ulcerative or nodular lesions. Carcinoma en cuirasse is characterized by extensive induration and sclerosis of the skin, resembling armor, and is a rare form of cutaneous metastatic carcinoma.

[PATIENT CONCERNS] We report a rare case of a 59-year-old patient who developed dark red nodules on the skin of the breast in 2013. These nodules gradually enlarged, ultimately causing the breast to lose its normal shape. Subsequently, the skin on the chest and back thickened, accompanied by local erosion and ulceration that gave the skin a hardened, armor-like appearance.

[DIAGNOSES] Ultrasound and chest CT suggest diffuse infiltration in the subcutaneous fat of the neck and thorax. Core-needle biopsy pathology reveals infiltrating micropapillary carcinoma, with tumor invasion of the dermis, the tumor clearly originates from the breast.

[INTERVENTIONS] The first-line treatment for advanced-stage breast cancer is the combination of cyclin-dependent kinase 4/6 inhibitors (CDK4/6 inhibitors) and aromatase inhibitors (AIs), specifically Abemaciclib and Anastrozole.

[OUTCOMES] The patient has been treated for 44 months, and the disease has significantly improved. This is evidenced by the absence of tumor tissue in the biopsy of the affected skin.

[LESSONS] Breast cancer cutaneous metastasis, although rare, requires high vigilance, especially in the HER2-negative Luminal B subtype. The efficacy data on CDK4/6 inhibitors combined with endocrine therapy as a standard regimen for cutaneous metastasis is still lacking. It is necessary to enhance mechanistic studies and clinical observations, taking molecular characteristics into account.