Breast squamous cell carcinoma (SCC) is a rare form of breast cancer and is highly malignant. It is defined by the World Health Organization (WHO) as “a breast carcinoma entirely composed of metaplastic squamous cells that may be keratinizing, nonkeratinizing, or spindled; neither derived from the overlying skin nor representing metastases from other sites” [1].

It is characterized by a rapid evolution and an uncodified treatment [2]. Due to the rarity of this neoplasm, data on its diagnosis, treatment, and prognosis are limited [3].

We report a new case of SCC of the breast, we will emphasize through a review of the literature the characteristics of this particular form of breast cancer.

Mrs Q.H., a 53-year-old, mother of 1 child living by vaginal delivery, menopausal for two years, consulted for further management of a left breast neoplasm.

The history of the disease goes back to one year and a half with the autopalpation of a nodule of the left breast, the initial clinical examination finds a mass of 5 cm at the junction of the left upper quadrants mobile, the initial echo-mammography objectified a suspicious lesion at the union of the left upper quadrants, measuring 30×21 mm, classified as Breast Imaging-Reporting and Data System 5 by the American College of Radiology (Figure 1), the biopsy with the trucut showed a well-differentiated keratinizing epidermal mammary carcinoma with the presence of carcinomatous lymphangitis, hormone receptor negative, Human Epidermal Growth Factor Receptor positive, Ki 67 = 30%.

The extension workup did not find any suspicious secondary lesions. The patient received 6 courses of neoadjuvant chemotherapy, based on taxanes and trastuzumab (end of 26/10/22) then once the chemotherapy sessions were over, the patient was referred for surgery.

The current clinical examination did not reveal any palpable mass or inflammatory sign or nipple discharge in both breasts. Post-chemotherapy ultrasound mammography showed regression of the lesion straddling the upper left quadrants measuring 23×15 mm classified as Breast Imaging-Reporting And Data System 6 by the American College of Radiology (Figure 2).

She was scheduled for a left mastectomy with sentinel lymph node. Unfortunately, the patient died following a pulmonary tuberculosis added to the immunodepression chemo induced.

Squamous cell carcinoma of the breast is an infiltrating ductal carcinoma with squamous cell-like metaplastic changes, in the absence of any other ductal or mesenchymal neoplastic component and other distant SCC sites [2].

The concept of a continuum of disease with varying degrees of squamous metaplasia has been supported by Stevenson et al. who conclude that SCC primarily represents an extreme form of squamous metaplasia within adenocarcinoma. Another theory is that these tumors arise directly from the epithelium of the mammary ducts [4].

Pure primary squamous cell carcinoma of the breast has been diagnosed in adult women aged 29–90 years. No cases have been described in men. It tends to be relatively large (>4 cm) at diagnosis and cystic in 50% of cases. Some authors have noted only rare lymph node involvement [5].

There are no specific features of primary SCC on mammography or ultrasonography [2], but sometimes ultrasonography can show a complicated cyst or an inflammatory process [5].

Immunohistochemistry shows expression of high molecular weight cytokeratins in epithelial tumor cells, including CK14, CK5/6, and CK17. However, the majority of these tumors do not express hormone receptors, which is consistent with our patient, and Human Epidermal Growth Factor Receptor 2 amplification is often absent. On the other hand, the proliferative character (Ki 67) has been strongly demonstrated by the study conducted by Grenier et al. [6],[7].

Treatment does not differ from other histological types of breast cancer and may involve surgery, chemotherapy, hormonal therapy, and radiotherapy. Due to its rarity, the most appropriate therapeutic regimen is not yet clear [4],[8].

As for metastasis, SCCs are thought to have less lymphatic spread than adenocarcinomas. In 10–30% of cases, there is lymph node infiltration at the time of surgery. In contrast, about 30% of patients will develop distant metastases [1].

Researchers believed that this type of tumor was highly invasive and that its prognosis was worse than that of typical triple-negative breast cancer. SATO’s research showed that patients with SCC of the breast had a median overall disease-free survival of only 20 months; and the 5-year disease-free survival rate was 26%; and the 5-year overall survival rate was only 40%.

Prognostic factors included age, surgical procedure, number of positive lymph nodes, primary site, and tumor size [2].

Pure SCC of the breast is a rare but generally aggressive disease. Current surgical management is similar to that of the more common adenocarcinoma. The etiology and pathogenesis of SCC of the breast is still unclear. Clinical trials including large series of these rare tumors are needed to increase our knowledge and to improve patient’s outcome.