Phyllodes tumors constitute less than 1% of breast tumors and 2–3% of fibroepithelial breast tumors 1. They usually occur in middle-aged to elderly women but can occur at any age. No single feature is reliable in predicting clinical behavior of phyllodes tumors. Several histological parameters should be evaluated, including stromal cellularity, atypia, mitoses, stromal overgrowth, infiltrative borders, and presence or absence of necrosis 12. A mitotic rate of less than 5 per 10 high power field (HPF) suggests benign behavior, while a mitotic figure rate of more than 10 per 10 HPF suggests malignant potential 23. Most of these tumors are benign, but up to 30% show malignant stroma 4. Metastases, usually hematogenous rather than lymphatic, have been reported to occur at a rate of 13% in 10 years for malignant phyllodes tumors 4. As malignant phyllodes tumors usually spread by a hematogenous rather than a lymphatic route, axillary lymph node dissection is generally not recommended. Importantly, local recurrences are common even in benign tumors and are seen in up to 8% in 10 years 4.

We describe a case of in-situ and invasive carcinoma occurring within a benign phyllodes tumor in a 26-year-old woman, which, to our knowledge, is the youngest presenting age for this combination tumor. We also report the first case of this combination tumor with documented lymph node metastases. Our case highlights the importance of assessing phyllodes tumors for concurrent carcinomatous involvement, as this may affect both the need for axillary lymph node examination and subsequent treatment options.

A 26-year-old woman presented with a 1 month history of a palpable mass in her left breast. Her mother died at the age of 31 years of breast cancer. Examination revealed a 2 cm firm and mobile mass in the lower outer quadrant of the left breast. The left axilla contained two enlarged palpable lymph nodes.

Mammography showed a 2 cm oval density that was homogenous with sharp margins. Ultrasound characterized the mass as solid but with a complex internal architecture. Fine needle aspiration of the mass was performed. It was positive for carcinoma, showing a very cellular sample with many malignant epithelial cells in cohesive groups, as well as lying singly in a background of necrosis and inflammation. The surgeon subsequently performed an excisional biopsy.

Grossly, the excised mass measured 3.3 cm × 2.3 cm × 2.0 cm and appeared well circumscribed. The cut surface was grey and lobulated with variable fleshy and firm areas. Histological examination revealed a well-circumscribed biphasic neoplasm, consisting of proliferating stroma and compressed glands, displaying a well developed leaf-like architecture. The stroma was moderately cellular, mildly vascular, and lacked cytological atypia, mitoses, and stromal overgrowth. The features were consistent with a benign phyllodes tumor (figures 1 &2). More importantly, the epithelial component of the phyllodes tumor showed extensive ductal carcinoma in-situ, with multiple foci of invasive mammary carcinoma (figure 3). The DCIS was of high nuclear grade, cribriform and micropapillary architecture, with (comedo-type) necrosis (figure 4). The invasive carcinoma was of no special type, SBR Grade III/III (Score 8/9). Multiple tumor emboli were present within endothelial-lined spaces adjacent to the tumor, but the surrounding breast was otherwise unremarkable. Although the carcinomatous component was confined to the phyllodes tumor, the lesion was <1 mm from the nearest resection margin. Immunohistochemistry using smooth muscle myosin heavy chain and muscle specific actin demonstrated absence of the myoepithelial cell layer within areas of invasive carcinoma, and focal loss within areas of DCIS. There was intensely positive staining within 80% of tumor cells for estrogen and progesterone receptors.

The patient went on to have a left axillary lymph node dissection and subsequent pathological examination revealed 4 of 13 nodes positive for metastatic adenocarcinoma. She received adjuvant CEF (Cyclophosphamide, Epirubicin, 5-Fluorouracil) chemotherapy and underwent further local excision to achieve wider margins; pathological examination was negative for residual tumor. She subsequently received local radiation and is currently undergoing tamoxifen therapy. The patient is presently alive and disease free, nearly three years after presentation.

The epithelial component of phyllodes tumors (whether benign or malignant) may show a range of metaplastic (apocrine, squamous) and proliferative changes 56. However, carcinoma arising within a phyllodes tumor is decidedly rare, with less than 30 reported cases in the literature. The age of the previously reported patients with coexistent carcinoma and phyllodes tumor ranged from 31–80 years, with most of the patients in the 5th or 6th decades 78. This case represents the youngest age at presentation with this combination tumor. The reported subtypes include in-situ and invasive lobular and ductal (no special type) carcinoma, tubular carcinoma and squamous carcinoma 234567910111213. Some authors have noticed greater atypia in epithelial components of recurrent phyllodes tumors. Squamous carcinoma, typically rare in the breast, seems to occur more often in phyllodes tumors, compared to patients without phyllodes tumors 10.

The prognosis for cases of carcinoma within phyllodes tumors is generally favorable, with no deaths yet reported 910. The stroma is benign in the majority and cancer detection often occurs early because the patient presents with a rapidly enlarging mass 10. Our case appears to represent the first documentation of lymph node spread of the carcinomatous component from within a phyllodes tumor. Axillary lymph node dissection is not part of the standard treatment for phyllodes tumors as lymph node spread is rare 14. Several authors have suggested treating carcinoma within phyllodes tumors according to the carcinomatous component 914. Our case supports this view, particularly with respect to the need for assessment of axillary lymph node status in determining prognosis and treatment.

Invasive carcinoma occurring within a phyllodes tumor is rare; occurrence of axillary lymph node metastasis is even rarer. Besides the stromal component, the epithelial component of phyllodes tumors should also be examined in detail, as it may harbor an in situor invasive carcinoma.