Carcinoma en cuirasse mimicking dermatomal herpes zoster: A case report

Introduction

Carcinoma en cuirasse (CeC) is a rare manifestation of cutaneous metastasis characterized by progressive sclerodermoid induration of the skin, most commonly arising in association with breast carcinoma. The term carcinoma en cuirasse was first described by Velpeau in 1838 and refers to a distinct form of cutaneous metastasis characterized by diffuse sclerodermoid induration resembling the steel breastplate worn by cavalry soldiers (cuirassier). ¹ Its clinical presentation may be variable and can mimic infectious, inflammatory, or treatment-related dermatoses, contributing to diagnostic delay. Histologically, CeC is characterized by interstitial infiltration of tumor cells in a single-file or linear cord arrangement in the dermis with secondary fibrosis of the stroma. ² We report a case of CeC presenting in a dermatomal distribution initially suspected to represent herpes zoster, highlighting an uncommon and misleading presentation of this aggressive metastatic process.

Case report

A 58-year-old woman was admitted to hospital for surgical management of pathologic spinal fractures requiring neurosurgical intervention in the setting of metastatic breast cancer. Her medical history was notable for estrogen receptor (ER)-positive, progesterone receptor (PR)-negative, and HER2-negative invasive lobular carcinoma with oncogenic PIK3CA p.Glu542Lys and p.His1047Arg mutations, as well as known bone and liver metastasis diagnosed 2 years and 3 months earlier. Additional comorbidities include hypertension and osteoporosis. Prior oncologic treatment consisted of three separate rounds of palliative radiotherapy of her lumbar spine and lateral ribs, in addition to ongoing treatment with letrozole and ribociclib initiated 1 month post diagnosis. She was also started on zoledronic acid at the same time but stopped 2 years post diagnosis in the setting of new pathologic spinal fracture requiring radiotherapy. Treatment history is outlined in Figure 1 and were generally well tolerated, with stable disease for the following 2 years prior to admission. On day of admission (DOA) 54, she was noted by her primary team to have developed a mildly pruritic eruption of grouped erythematous papules and plaques in a dermatomal distribution on her right flank with no vesicles. Notably, she had never received radiotherapy to this area. Infectious diseases was remotely consulted and localized herpes zoster involving multiple adjacent dermatomes was suspected in the setting of relative immunosuppression with ongoing ribociclib use. She was empirically started on a 14-day course of valacyclovir 1 g oral three times daily, although viral polymerase chain reaction (PCR) swab was not collected at the time. Although she reported partial symptomatic improvement, the eruption persisted beyond completion of treatment, following which she developed new lesions of the right flank on DOA 76, prompting repeat infectious diseases consultation. Infectious diseases noted the lesions were indurated and lacked crust, which they felt was atypical of shingles or cellulitis; therefore, dermatology was consulted. Viral PCR swabs were collected and later returned negative. Cutaneous examination at the time of consult revealed diffuse induration of the right breast, flank, and mid-back, predominantly along the T5–T7 dermatomes with erythematous nodules coalescing into a sclerodermoid plaque (Figure 2).

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Figure 1.

Case report timeline. Presented according to CARE guidelines.

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Figure 2.

(a, b) Skin eruption shown at the time of consultation (a) and 2 months later (b).

Skin biopsy demonstrated infiltration of the dermis by discohesive monomorphous atypical epithelial cells with vacuolated cytoplasm, arranged in a characteristic single-file pattern and in clusters, with involvement of adnexal structures and perineural spaces (Figure 3). Immunohistochemical staining showed strong positivity for cytokeratin 7 (CK7) and ER, with absence of CK20 expression. The National Comprehensive Cancer Network 2026 Guidelines listed the expected breast carcinoma profile as CK7+, CK20−, GATA3+, GCDFP-15 mammaglobin+, and TRPS1+, in addition to variable positivity in ER/PR. ³ Based on the combined clinical and histopathological findings, a diagnosis of CeC was established on DOA 80. Ribociclib had previously been held on DOA 63 by Medical Oncology due to concerns of ongoing infection. Following confirmation of the diagnosis, ribociclib was reinitiated on DOA 84; however, it was subsequently discontinued on DOA 99 due to ongoing normocytic anemia attributed to the medication. A bone scan was performed on DOA 107 demonstrating progression of existing bone metastasis and appearance of new osseous lesions. Treatment with denosumab was initiated for prevention of skeletal-related events in the setting of bone metastasis. On DOA 108, systemic treatment was escalated in the setting of disease progression in the form of new cutaneous metastasis and worsening bone metastasis. She was started on fulvestrant and capivasertib 14 days later as indicated by the CAPItello-291 trial in patients with PIK3CA, AKT1, or PTEN(Phosphatase and TENsin homolog) pathway alterations. ⁴ The patient was discharged from hospital on DOA 116; however, she was readmitted 45 days later with a suspected upper gastrointestinal bleed and severe anemia requiring transfusion. Ten days following readmission, magnetic resonance imaging of the brain showed dural metastases. Sixteen days into admission she was transitioned to comfort care and discharged 2 days later into hospice care. Eight days after discharge she passed away.

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Figure 3.

(a, b) H&E sections showing diffuse infiltration of the dermis by epithelial cells arranged in single-file lines, shown at low magnification (a) and high magnification (b). (c, d) Immunohistochemical staining for estrogen receptor demonstrating strong nuclear positivity in the neoplastic cells, shown at low magnification (c). Scale bars: 500 µm (a, c), 60 µm (b, d).

Discussion

Although most commonly associated with breast carcinoma, CeC has been reported in association with other primary malignancies, including lung, kidney, gastrointestinal, and urothelial cancers.^{5 –7} CeC is seen in ~3% of patients with cutaneous metastasis from breast cancer. ⁸

Clinically, CeC can be difficult to distinguish from infectious, inflammatory, and treatment-related conditions including skin infections, radiation dermatitis, or morphea. Lesions often begin as erythematous papules or nodules before progressing to an indurated, sclerodermoid plaque. Dermatomal or zosteriform distributions, as seen in this case, may further obscure the diagnosis and delay appropriate evaluation.

Histopathologic examination typically reveals interstitial infiltration of tumor cells in “single-file” lines within a densely fibrotic stroma, often with reduced vascularity. ⁶ The “single-file” pattern is a hallmark of invasive lobular carcinoma due to a loss of E-cadherin resulting in cell discohesion and a linear cord arrangement. ⁹ Immunohistochemistry is essential in confirming tumor origin, particularly in patients with known metastatic disease. ⁶

Management of CeC is challenging, as impaired microvasculature may limit penetration by systemic therapies and radiation. There is no established standard of care, and treatment is generally palliative, incorporating systemic chemotherapy, local radiotherapy, hormonal manipulation, or surgical approaches aimed at symptom control and preservation of quality of life.^5,6 Prognosis varies according to the primary malignancy; among patients with breast cancer, median survival following diagnosis of CeC has been reported at ~13.8 months. ⁶

This case highlights CeC as an important diagnostic consideration in patients with persistent or atypical dermatomal eruptions, particularly in the setting of known malignancy, and reinforces the critical role of dermatologic assessment and skin biopsy in the avoidance of diagnostic delay.