Fig. 2: Practical approach classification

Reactive and neoplastic mesenchymal and epithelial/myoepithelial lesions that can be classified as: 

1.1. Lesions of mesenchymal fibroblastic/myofibroblastic origin.

1.1.1. Scar Fig. 3 .

It is the most frequently found spindle cell lesion.

Presentation. Breast retraction, usually with a history of surgery or trauma.

Mammogram. Architectural distortion. Associated findings. Skin retraction

US. irregular hypoechoic mass with posterior shadowing sometimes mimicking malignancy.

MR. Imaging of postsurgical scars on MR varies depending on when the actual surgery was performed. In most cases, enhancement within the biopsy bed is seen up to 12 months after surgery.

Pathology. Hemosiderin, foreign body cells, fat necrosis.

Immunohistochemistry (IHC). positive for SMA, but negative for b-catenin, desmin, and CD34.

Fig. 3: Scar: 46 yo woman. Fibroadenoma excision 20 years ago. Mammogram. Architectural distortion. US. Hypoechoic ill-defined area (arrow). Gross specimen. Scar.

1.1.2. Fibromatosis Fig. 4 .

It is an infiltrative locally aggressive proliferation  of fibroblasts/myofibroblasts.

Presentation is usually a painless slow-growing ill-defined mass.

Mammogram, US. Ill-defined  or spiculated mass. It may simulate carcinoma.

MR. Masses, Isointense on T1-weighted and lower or higher intensity lesions on T2, usually with heterogeneous contrast enhancement atypical for carcinoma.

Path. Gross features are sometimes a stellate lesion.

IHC: . Negative for CD34, CKs, p63, desmin, and S100.

Fig. 4: Fibromatosis. 41 yo woman. Palpable mass. Mammogram. Dense mass with angulated margins. US. Heterogeneous mass with irregular margins. HE. Spindle cells. Fibromatosis.

1.1.3. Nodular fasciitis Fig. 5 . 

Benign proliferation of fibroblasts and myofibroblasts, frequently located in the deep subcutaneous region or in the fascia.

Presentation. Tender or painful rapidly growing breast mass.

Mammogram. Circumscribed or irregular masses sometimes mimicking malignancy.

US. Irregular, non-circumscribed hypoechoic nodules.

MR. Irregular margins and contrast enhancement may appear.

Path.Well-circumscribed lesion composed of fibroblasts. Mitosis may be frequent, but no abnormal forms appear.

IHC: positive for actin.

Fig. 5: Nodular fasciitis. 49 yo woman. Palpable mass. Mammogram. Dense circumscribed nodule in the axillary area. US. Hypoechoic nodule with circumscribed margins. Features not suggesting a lymph node. Gross specimen. White circumscribed nodule.

1.1.4. Myofibroblastoma Fig. 6  and Fig. 7 .

Myofibroblastoma is a benign proliferation of myofibroblasts, no recurrence is found. Incidence is similar in males and females.

Presentation is a mobile, slow growing mass.

Mammogram, US: Circumscribed mass, usually smaller than 4 cm.

MR. Circumscribed homogeneously enhanced mass with internal septations

Path. Gross specimen . Lobulated, circumscribed, no true capsule.

IHC: positive for CD34, desmin, SMA, ER, PR, CD99, bcl-2, and CD10.

Fig. 6: Myofibroblastoma. 42 yo woman. Palpable mass on breast tail. US. Vascular heterogeneous mass with circumscribed margins. MR. T2 Hyperintense, Gadolinium enhancement. Gross specimen. White lesion H-E stain. Myofibroblastoma.

Fig. 7: Myofibroblastoma. 86-yo man. Palpable mass. Mammogram. Lobulated mass. US. Heterogeneous mass with circumscribed margins. Gross specimen. White lesion.

1.1.5. Pseudoangiomatous stromal hiperplasia (PASH) Fig. 8 . 

It is a benign stromal localized mesenchymal stromal cell overgrowth.

Presentation. Premenopausal women,  painless mass.

Mammogram, US. Circumscribed mass. In certain cases subtle focal asymmetry on mammograms or no findings.

MR. Non-mass enhancement, no findings or mass.

Path. It appears usually as an incidental finding in the shape of a microscopic focus, but it may show mass appearance and histopathology simulating a fibroepithelial tumor: solitary, multifocal nodules or as a diffuse massive process with asymmetry of the breast.

Fig. 8: Pseudoangiomatous stromal hyperplasia (PASH). 17 yo woman. Palpable mass. Mammogram. Circumscribed dense mass. US. Homogeneous slightly hyperechoic mass. Gross specimen. White lesion. H-E stain. Nodular PASH.

1.2. Fibroepithelial lesions. Benign phyllodes tumor Fig. 9 .

Phyllodes tumors are biphasic lesions, with different types of specialized or non-specialized stroma.

Presentation. At presentation  both benign and malignant phyllodes tumors are enlarging breast masses. Recurrence may appear in all cases.

Mammogram. Circumscribed mass.

US. Smooth margins and heterogeneous mass sometimes with cystic areas.

MR. Circumscribed mass, contrast enhancement. In certain studies hyperintenseT1 lesions more frequently malignant. Iso and  hypointense T2 and low ADC correlated with stromal hypercellularity.

Path. Phyllodes tumours are diagnosed when the fibroepithelial architecture shows an exaggerated intracanalicular pattern with leaf-like fronds protruding into cystically dilated spaces accompanied by stromal hypercellularity. Fibroepithelial lesions are sometimes difficult to diagnose on core biopsy, so differential diagnosis is not always easy between phyllodes tumor and fibroadenoma. If a mass diagnosed as fibroadenoma on core biopsy, increases in size, excluding phyllodes tumor is mandatory .

Fig. 9: Benign Phyllodes Tumor 32 yo woman. Palpable mass. Mammogram. Mass with circumscribed and occult margins. US . Well circumscribed hypoechoic, nodule. Specimen. Benign phyllodes tumor.

1.3. Smooth muscle tumour. Leyomioma Fig. 10 .

Intraparenchimal leiomyomas of the breast are very rare, leiomyoma of the nipple  is a rare, but more common, benign neoplasm.

Presentation. Slowly growing mass.

Mammogram and US. An oval mass with circumscribed margins.

MR. Intermediate signal intensity on both T1- and T2-weighted images. A dynamic MRI study shows enhancement.

Path. Smooth muscle benign tumor. Free margins should be established to prevent recurrence.

IHC: positive for SMA, desmin, and caldesmon.

Fig. 10: Leyomioma 60 yo man. Palpable mass. US.Circumscribed hypoechoic superficial lesion in the areola.

2.1. Mammary epithelial tumors. High-grade spindle cell metaplastic breast carcinoma (MBC) Fig. 11 .

Spindle cell carcinoma is a type of metaplastic carcinoma(<1% carcinomas).

Presentation is similar to conventional carcinoma, tends to be larger and well-circumscribed masses. Typically ER, PR, HER 2 negative. Lymph node metastases are rare, more frequent hematogenous.

Prognosis poorer than for conventional carcinoma, behavior more similar to sarcoma.

Mammogram. Large mass sometimes with benign features: round or oval mass with circumscribed margins Pleomorphic, linear microcalcifications are rare.

US. oval, round, or lobular solid hypoechoic or heterogeneous mass with circumscribed or indistinct margins with posterior acoustic enhancement.

On MR, T2-weighted images show a relatively well-defined mass with high signal intensity. In the dynamic study, they usually present with contrast uptake, with signal-time intensity curves similar to those of infiltrating carcinoma of the breast.

Path. Histological diagnosis sometimes difficult, Caution specially on CNB.

IHC: positive for CKs. Positive for p63 in squamous areas. Typically negative for CD34, hormone receptor, and HER2. Variable degree of positivity for myoepithelial markers. 

Fig. 11: Metaplastic carcinoma Mammogram. Dense lobulated mass US Doppler. Multicystic mass with vascular area. MR . Cysts with fluid levels and area of enhancement. HE. Metaplastic carcinoma.

2.2. Mammary  myoepithelial tumors. 

Malignant adenomyoepithelioma and myoepithelial carcinoma Fig. 12 .

An adenomyoepithelioma is an epithelial–myoepithelial tumour, composed of myoepithelial cells surrounding epithelium lined spaces, giving a histological appearance of a balanced dual proliferation of two cell types. Either  or both epithelial and myoepithelial components can undergo malignant transformation, the latter exemplified by myoepithelial carcinoma arising within the background of an adenomyoepithelioma.

Clinical presentation is usually a palpable mass.

Mammogram. Round or irregular mass usually with indistinct margins and high density.

US. Hypoechoic mass

MR. Contrast enhancement mimicking breast carcinoma.

Path. solitary lesion, characterized by an infiltrating proliferation of atypical spindle cells.

IHC: positive for markers of myoepithelial differentiation, including SMA, myosin, p63, and S100.  

Fig. 12: Myoepithelial carcinoma

2.3. Primary breast sarcoma.

2.3.1. Malignant phyllodes tumor Fig. 13 and Fig. 14 .

Phyllodes tumours are classified into benign, borderline and malignant grade categories based on multiple histological parameters, i.e. the degree of stromal cellularity and atypia, mitotic count, stromal overgrowth, and the nature of their tumour borders. There is a risk of local relapse and distant metastases, in particular to the lung. Surgery is the standard treatment.

Presentation. At presentation  both benign and malignant phyllodes tumors are enlarging breast masses. Recurrence may appear in all cases.

Mammogram. Circumscribed mass, sometimes malignant features.

US. Smooth margins and heterogeneous mass with frequent cystic areas.

MR. Circumscribed mass, contrast enhancement. In certain studies hyperintenseT1 lesions more frequently malignant. Iso and  hypointense T2 and low ADC correlated with stromal hypercellularity.

Path. A malignant phyllodes tumour shows marked stromal cellularity and atypia, has permeative margins, and has mitotic activity of at least 10/10 HPFs. Stromal overgrowth is usually easily identified. The stroma of a malignant phyllodes tumour may, on occasion, show heterologous sarcomatous differentiation. Phyllodes tumours with intermediate features are assigned to the borderline category. Differential diagnosis of the malignant phyllodes tumour from spindle cell metaplastic carcinoma and primary breast sarcoma can be difficult.

Fig. 13: Border line Phyllodes tumor 48 yo woman. Palpable mass. Mammogram. Mass with occult margins. US . Well circumscribed nodule. Core biopsy. Atypia. Specimen. Border-line phyllodes tumor.

Fig. 14: Malignant Phyllodes tumor 45 yo woman. Palpable mass. Mammogram. Mass with circumscribed margins. US . Complex cystic mass with thick walls and solid areas. Specimen. Hypercellular stromal overgrowth , stromal cellular pleomorphism and a number of mitosis greater than five per 10 high-power fields Malignant phyllodes tumor.

2.3.2. Angiosarcoma Fig. 15 .

They are mesenchimal agressive malignant lesions frequently diagnosed after radiation therapy for primary breast cancer.

Presentation. Gradually progressive swelling is the most frequent presenting symptom.

On mammography they are non-specific usually large and progressively growing masses or asimmetric density.

On US they present as heterogeneous masses, usually solid hyperechoic or mixed hyperechoic and hypoechoic, highly vascular masses, but sometimes with wide anechoic cystic areas. They may also appear as diffuse abnormal mixed hyper and hypoechogenicity areas without a mass.

MR. Large, lobular masses heterogeneously hypointense on T1-weighted images and heterogeneously hyperintense on T2-weighted images, with irregular areas of high signal intensity on T1-weighted images (hemorrhagi) and common cystic cavities. Contrast enhancement is intense and heterogeneous, with a typical malignant pattern on dynamic contrast material–enhanced images.

Fig. 15: Angiosarcoma. 62 yo woman. Rapidly growing mass. Mammogram. Assimetric density in an enlarged breast. US. Infiltrating hypoechoic areas. Gross specimen . Angiosarcoma

2.4. Metastatic malignant spindle cell tumours. Melanoma Fig. 16  .

Melanoma is one of the most frequent tumors to metastasize in breast parenchyma.

Clinical history and immunohistochemistry are keys for diagnosis.

Mammogram and US. Solitary or multiple masses. Presence of multiple masses may indicate metastasis, but a solitary metastasis may also appear.

MR. Melanoma features may appear , Hyperintense on T1, contrast enhancement

IHC. Positive for S100 and vimentin.

Fig. 16: Metastatic melanoma. Mammogram. Dense mass with lobulated margins. US.Heterogeneous mass with irregular margins. HE. Melanoma.