Advanced, Recurrent Malignant Phyllodes Tumor With Malignant Heterologous Osteoid Differentiation Coexisting With Fibroadenoma in a 17-Year-Old Female Nigerian: A Case Report

Abstract

Fibroepithelial tumors of the breast are characterized by neoplastic proliferations of both ductal epithelial and stromal components of the breast parenchyma and exhibit biological behavior that ranges from completely benign to frankly malignant subtypes. Fibroadenoma, the prototypical benign example of these tumors, is both the most common benign tumor of the female breast overall and the most common breast tumor in adolescent and young adult females. Phyllodes tumor, on the other hand, encapsulates the full spectrum of benign to malignant biological behavior of these tumors, and while not as prevalent as fibroadenoma, it nevertheless occurs over a wider age range and is more prevalent in older females. The age incidence of phyllodes tumor also parallels its biological behavior, increasing as the spectrum progresses from benign to malignant. Fibroadenoma and phyllodes tumor share clinical and morphological characteristics, although they arise from different components of the breast parenchyma, the terminal duct lobular unit, and specialized periductal stroma. Furthermore, the malignant potential of phyllodes tumor makes its diagnostic distinction from fibroadenoma a clinical and prognostic imperative. We present the unusual case of a 17-year-old adolescent female, Nigerian, who was diagnosed with malignant phyllodes tumor of the left breast, with heterologous osteoid component, coexisting with an ipsilateral fibroadenoma, highlighting the importance of proper evaluation of breast masses regardless of patients' age.

Keywords: adolescent female; breast; fibroadenoma; heterologous malignant osteoid; malignant phyllodes tumor.

Figure 1. Malignant phyllodes tumor of the left breast showing malignant stroma and heterologous elements

(A) Note the haphazard fascicles of malignant spindle cells (black arrows) and areas of malignant osteoid deposition (red arrows) (H&E, x100). (B) Note the malignant osteoid deposition (red arrows) with atypical osteocytes seen within lacunar spaces and abnormal mitosis (brown arrow) (H&E, x200) (C). Note the malignant osteoid deposition (red arrows), atypical osteocyte with large vesicular nucleus (yellow arrow), and rhabdoid tumor giant cells (blue arrows) seen around the osteoid (H&E, x400) H&E: hematoxylin and eosin

Figure 2. Malignant phyllodes tumor of the left breast showing epithelial elements

(A) Note areas with borderline phyllodes features (green circle) adjacent to the areas of frankly malignant proliferating stroma (blue circle) (H&E, x40). (B) Note the borderline features magnified from image ‘A’, showing ducts and leaf-like structures lined by benign epithelium (blue and yellow arrows, respectively), surrounded by atypical stroma exhibiting subepithelial condensation (red arrows) (H&E, x200). (C) Note another portion of the tumor showing rare foci of benign epithelial components (yellow arrows), surrounded and compressed by proliferating malignant stroma (red arrows) (H&E, x400). H&E: hematoxylin and eosin

Figure 3. Immunohistochemistry of malignant phyllodes tumor of the left breast

(A) Patchily positive P63 stain; note nuclear staining (golden brown coloration) of lesional cells (P63 IHC, x400). (B) Diffusely positive BCL2 stain; note nuclear staining (golden brown coloration) of lesional cells (BCL2 IHC, x400). (C) Negative CD34 stain; note lack of staining of lesional cells and membranous staining (golden brown coloration) outlining vascular channels (CD34 IHC, x400). (D) Negative CK5/6 stain; note lack of staining of lesional cells (CK5/6 IHC, x400) IHC: immunohistochemistry

Figure 4. Fibroadenoma of the left breast

Note mixed intracanalicular and pericanalicular patterns of the epithelial elements composed respectively of elongated and compressed slit-like structures (blue arrows) and small ducts with empty lumina (red arrows), surrounded by proliferating fibromyxoid stroma (H&E, x200) H&E: hematoxylin and eosin

Figure 5. Recurrent left breast mass protruding through complete wound dehiscence

Figure 6. Recurrent malignant phyllodes tumor with heterologous malignant osteoid

(A) Note sheets, whorls, and fascicles of malignant spindle cells (green circles), and malignant osteoid deposition (yellow arrow) (H&E, x100). (B) Note atypical osteocyte with large vesicular nucleus (red arrow), and malignant osteoid deposition (yellow arrows) within lacunar spaces (H&E x400) H&E: hematoxylin and eosin

Figure 7. Preoperative photograph showing multiple, recurrent left chest wall nodules

Figure 8. Advanced recurrent malignant phyllodes tumor with heterologous malignant osteoid

(A) Note atypical spindle cells (red arrows) and sheets of atypical epithelioid cells (blue circle) (H&E, x200). (B) Note the malignant osteoid deposition (yellow arrows) and large, bizarre, tumor giant cell with enlarged hyperchromatic nuclei (green arrow) (H&E, x400). H&E: hematoxylin and eosin