Myofibroblastoma arising in the mammary gland is a rare benign disease first described by Wargotz et al [1]. In 1987. It tends to occur in middle-aged and older patients with clinically suspected malignancy, and it is image- and histologically diverse [2-4]. Surgery according to malignancy may be performed without a definitive diagnosis [5]. We report a case in which a myofibroblastoma diagnosed before surgery, and the patient underwent excisional biopsy.

A 76 years old man

Chief complaint: left breast mass

Physical history: Treated for type 2 diabetes since the 50s.

Family history: No family history of cancer

Current medical history: Patient was pointed out a left breast mass on CT performed due to coughing symptoms.

Palpation findings: A 4 cm in diameter mass was palpated in the outer upper part of the left breast, slightly away from the nipple. It had the consistency of a pseudolipoma and no skin findings. No lymph nodes were palpable.

Mammographic findings: Category 4 with a high density mass with irregular margins in the left outer upper quadrant.

Ultrasonographic findings: A 23 mm in diameter hypoechoic mass was seen in the same area. The internal echo was relatively homogeneous with partially irregular borders and a thick halo around it. Infiltration of the surrounding fatty tissue was suspected. There were no enlarged lymph nodes.

CT: A nodule was seen in the outer upper part of the left breast, and a series of thin striated hyperabsorptive areas were seen toward the nipple.

Fine needle aspiration cytology findings: difficult to differentiate (Class III)

No clear ductal epithelial cells were observed. Small, spindle-shaped to fibrous, fibroblast-like cells were seen in scattered to clustered clusters. A non-epithelial (stromal) neoplastic lesion was suspected.

Core needle biopsy histology: Bundled proliferation of spindle-shaped cells with elongated eosinophilic vacuoles and oblong or ellipsoid nuclei were observed from between collagen fibers and partly in the marginal adipose tissue. Immunostaining was estrogen receptor (ER) positive, progesterone receptor (PgR) positive, Ki67 was almost 1%, and negative for cytokeratins (AE1/AE3, CK5/6) and p63. The possibility of mesenchymal tumor, especially myofibroblastoma, was considered, and immunostaining was added.

Spindle-shaped cells were positive for desmin, CD34, STAT-6 (negative in nucleus, positive only in cytoplasm) beta-catenin (negative in nucleus, positive only in cytoplasm), and almost negative for EMA, findings that support myofibroblastoma.

Surgery: Some cases with a tendency to enlarge were reported, and tumor excision including surrounding fatty tissue was performed for complete resection [6].

Histopathology: Split surface showed a well-defined white nodular mass of 26x11mm in size, centered on a resected lesion.

There was an infiltrative proliferation of spindle-shaped cells against the adipose tissue, but a thin fibrous capsular structure was formed at the margins of the lesion. The lesion was consistent as a myofibroblastoma, as noted on needle biopsy. A fatty component was predominant, suggesting a lipomatous subtype. In addition, scattered ducts were observed at the nipple lateral margin, but no malignant findings were noted.

Figure 1: a,b) Mammography Showed A High-Density Mass In The Left Breast.

c) The Ultrasound Examination Revealed A Hypoechoic Mass With A Thick Halo.

d) A CT Scan Also Showed A Highly Absorbent Mass In The Left Breast.

Figure 2: a) The Cytological Examination Revealed Spindle-Shaped Cells.

b,c,d) A Needle Biopsy Also Revealed Spindle-Shaped Cells, But No Findings Suggestive Of Malignancy Were Observed.

Figure 3: a) AE1/AE3 Was Negative.

b) CK5/6 Was Negative.

c) CD34 Was Positive.

d) Desmin Was Positive.

Figure 4: a) Louped Image of the Extracted Specimen

b) The Spindle-Shaped Cells That Had Increased Were Consistent With The Findings Of The Needle Biopsy.

c) Adipose Tissue at the Tumour Margin.

d) Section of an Extracted Specimen.

Myofibroblastoma arising in the mammary gland is a rare benign disease first described by Wargotz et al. in 1987 [1]. Besides the breast, it has been found to occur more frequently in the so-called milkline, from the axilla to the inguinal lesion [7]. The most common sites are the inguinal lesion and scrotum (45%), while the breast is reported to account for 10% of all cases [8]. Both sexes are reported to occur more frequently in the 40-80 years old, with postmenopausal women and older men [2,3]. There are also prominent reports that it is more common in men, but some reports in women [9,10]. There is no association with race, comorbidities, oral medications, or hormonal agents [11].

The most common reasons for detection are painless mass awareness and detection by medical examination [12], and in this case, the tumor was discovered on CT scan that was performed to search for other diseases. The average diameter of tumors arising in the breast area is 23-66 mm and cases of rapid growth have been reported [6].

Mammography and ultrasonography often show a well-defined, round, lobulated mass [6,9,13,14]. Cytology and needle biopsy specimens show spindle-shaped cells, which may lead to the diagnosis of phyllodes tumor or benign mesenchymal tumor [10]. In some cases, when the cells were of different sizes or had irregular nuclei, malignant phyllodes tumor [13], invasive lobular carcinoma, or spindle cell carcinoma was suspected, and surgery was performed [5,15].

Histopathologically, spindle-shaped cells are seen against a background of collagen bundle growth, and immunostaining is positive for CD34, Vimentin, CD10, CD99, ER, PgR, and BCL-2 protein. In addition, desmin, SMA, and Androgen receptor are often positive; CD117 (C-kit), EMA, and S-100 are negative. It is also reported that nuclear Rb staining is negative in more than 90% of cases [8,10,12].

Immunostaining of spindle-shaped cells in this case also showed positive results for Vimentin, CD34, ER, and PgR, and negative results for epithelial markers AE1/AE3 and EMA, findings that support myofibroblastoma.

The WHO classification (Breast Tumors. 5th edition) divides them into five subtypes based on the composition of spindle-shaped cells and stromal cells: lipomatous, myxoid, fibrous/collagenized, epitheloid/deciduoid, palisading/ Schwannian-like pattern [12]. The present case was considered to have a lipomatous pattern, which shows a fatty tissue infiltration pattern.

Myofibroblastoma is difficult to diagnose accurately by H.E. staining alone due to the great diversity of histology by subtype. It was thought that myofibroblastoma could be listed as a differential based on the presence of spindle-shaped cells, and a definitive diagnosis could be obtained with appropriate immunostaining to prevent excessive surgery.

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