Phyllodes tumor is a rare fibroepithelial neoplasm, but the occurrence of cystic squamous metaplasia is very uncommon. Tan et al, found epithelial squamous metaplasia in 12 cases from 335 reported cases, 5 (1.5%) of which revealed squamous metaplasia cysts [5]. Phyllodes tumor is usually diagnosed in women aged 31–49 years [6]. Clinically, it usually manifests as a mobile, unilateral, single, painless and rapid growing mass [6, 7]. The size of phyllodes tumors is quite variable but the median size is usually around 4 cm. The mass exceeding 10 cm is considered as a giant tumor [4]. The giant tumors distort the breast and may cause skin manifestations, such as an ulceration [7]. This cited case is similar to our patient who presented with a giant ulcerated tumor. There is no significant relationship between phyllodes tumor size and histopathological sub-groups. Rapid growth may be detected in malignant tumors [8]. Radiologically, the imaging features of breast phyllodes tumor are nonspecific and appear as a well-circumscribed oval or lobulated mass with rounded borders [9]. It may be difficult to distinguish phyllodes tumor from cellular fibroadenoma, cysts, lipoma, hamartoma, sarcoma, well-circumscribed carcinoma and metastasis [7, 10]. Therefore, the histological examination remains the cornerstone of phyllodes tumor diagnosis and the establishment of histopathological subgroups.
Grossly, phyllodes tumor usually appears as lobulated tumor, with grey or red “meaty” consistency, with haemorrhagic, fibro gelatinous, necrotic areas on cut section [11]. Phyllodes tumor is characterized by leaf-like phyllodes structures lined by double layered epithelium, an internal epithelium with a myoepithelium outside, that has cleft-like cystic spaces with hypercellular stroma and intracanalicular growth pattern [5].
Once the diagnosis of phyllodes tumor is made, it classified as benign, borderline, or malignant according to the features, such as tumor margins, stromal overgrowth, tumor necrosis, cellular atypia, and amount of mitosis per high power field (hpf). Benign phyllodes tumors show stromal cellular increase, mild-to-moderate atypia, mitosis < 4 /10 hpfs, and the tumor has regular borders without stromal overgrowth. Borderline phyllodes tumors have more stromal cellular proliferation and atypia, with infiltrating borders, a mitotic count of 4–9/10 hpfs, but without stromal overgrowth. Malignant phyllodes tumors have significant stromal cellular proliferation and atypia, mitotic count is ≥ 10/10 hpfs, with infiltrating margins and stromal overgrowth [8]. The most common grade of phyllodes tumor is benign, they occur in 60–75% of the cases [12]. The various changes can occur in the different components of phyllodes tumor. In the stromal component, pseudoangiomatous stromal hyperplasia, cartilaginous, osseous, lipomatous metaplasia or stromal giant cells can be seen. The epithelial component can undergo squamous or apocrine metaplasia but those changes are very uncommon [5]. In the present case, we have a squamous metaplasia arising in the benign phyllodes tumor. The development of squamous metaplasia in breast was suggested to begin within the myoepithelial cell layer, before eventually involving the entire acinus. This myoepithelial origin of the metaplastic squamous cells has been supported by the immunohistochemical studies, which showed expression of actin, vimentin and S-100 protein in the metaplastic squamous cells [13].
The standard treatment for these tumors is surgical resection with tumor-free margins of one centimeter or larger to decrease the rate of recurrence. If the negative margins cannot be guaranteed through conservative surgery, simple mastectomy is recommended [11].
In conclusion, cystic squamous metaplasia is a rare feature of phyllodes tumor. It is essential to be aware of this uncommon event in order to avoid misdiagnosis.