Breast myofibroblastoma (MFB) is a rare benign mesenchymal stromal tumor first described by Wargotz and Norris in 1987 [1]. It is typically observed in older men and postmenopausal women, although cases in premenopausal women have also been reported [2][3]. The occurrence of MFB during pregnancy is exceptionally uncommon, with only isolated cases described in the literature [4][5].

Histologically, MFB is characterized by a well-circumscribed proliferation of uniform spindle-shaped cells arranged within a collagenous or variably myxoid stroma, sometimes associated with adipocytic components [6][7]. Immunohistochemistry is essential for establishing the diagnosis, as tumor cells commonly express desmin and CD34 and may show hormone receptor positivity, while remaining negative for epithelial markers such as cytokeratins and p63 [8][9]. This immunophenotypic profile is critical for distinguishing MFB from other spindle-cell lesions of the breast, including spindle cell lipoma, fibromatosis, and metaplastic carcinoma [10][11].

Clinically and radiologically, MFB may mimic malignant breast tumors. Imaging typically reveals a well-defined mass; however, heterogeneous echotexture or increased vascularity may lead to a BIRADS 4 classification and raise suspicion for malignancy [5][12]. This diagnostic overlap becomes even more challenging during pregnancy, when physiological hormonal changes alter breast density and vascularity, potentially masking or exaggerating pathological findings [4].

Complete surgical excision is considered curative, with extremely low recurrence rates and no documented malignant transformation [9][13][14]. Nevertheless, in pregnant patients, the timing of surgery must be carefully individualized. Multidisciplinary evaluation is essential to balance oncologic safety with maternal and fetal well-being, particularly in late gestation [5].

In this context, we report a rare case of breast myofibroblastoma diagnosed during the third trimester of pregnancy, highlighting the diagnostic challenges and rationale for delayed surgical management.

A 32-year-old woman, gravida 3 para 2, presented at 33 weeks of gestation with a progressively enlarging exophytic mass of the left breast that had evolved over four months, coinciding with her current pregnancy. She had no significant past medical history and no family history of breast or ovarian malignancy.

Physical examination revealed a large, mobile, non-tender exophytic lesion centered on the nipple. The overlying skin was intact, with no signs of ulceration or inflammation (Figure 1Figure 1).

Breast ultrasound performed on August 18, 2025, revealed a hypoechoic, heterogeneous, vascularized mass measuring 55 × 48 mm. The lesion was classified as BIRADS 4C. Additional peri-areolar nodules and ductal ectasia were observed. No axillary lymphadenopathy was detected [5][12].

Ultrasound-guided core needle biopsy demonstrated a spindle-cell mesenchymal proliferation composed of uniform elongated cells embedded within collagenous stroma. Immunohistochemical analysis showed strong desmin expression, focal CD34 positivity, and negativity for p63, pancytokeratin, CK5/6, and β-catenin. These findings confirmed the diagnosis of breast myofibroblastoma [6]-[10].

Following multidisciplinary discussion, surgical excision was deferred due to confirmed benign pathology and advanced gestational age. The patient was monitored clinically until delivery. She delivered a healthy neonate at term via spontaneous vaginal delivery without complications. Postpartum evaluation confirmed lesion stability, and surgical excision was scheduled six months after childbirth (Figure 2Figure 2).

Figure 1. Clinical photograph demonstrating a prominent exophytic nipple mass of the left breast.

Figure 2. Postpartum clinical image (day 10) showing persistence of the exophytic nipple mass.

Breast myofibroblastoma is a rare benign stromal tumor with characteristic immunohistochemical features [1][9]. Although more common in older individuals, its occurrence during pregnancy is exceptional [3][5]. Hormonal influences may contribute to tumor enlargement during gestation.

Breast myofibroblastoma during pregnancy is a rare condition that may mimic malignancy and create diagnostic uncertainty. Core needle biopsy combined with immunohistochemistry is essential for accurate diagnosis. When benign pathology is confirmed, delayed surgical excision until the postpartum period may safely balance oncologic control with maternal-fetal well-being. Multidisciplinary management is crucial in optimizing outcomes.