Diagnostic and Therapeutic Challenges in Pseudoangiomatous Stromal Hyperplasia (PASH) of the Breast in a 14-Year-Old Girl: A Case-Based Review.

Introduction: Pseudoangiomatous stromal hyperplasia (PASH) is a benign breast lesion characterized by stromal myofibroblast proliferation forming slit-like pseudoangiomatous spaces. Although most frequently diagnosed in premenopausal women, it has also been reported in adolescent girls, where it may present as a rapidly enlarging mass that mimics fibroadenoma or phyllodes tumor. The pathogenesis is thought to be hormonally influenced, particularly by progesterone, with a possible role for estrogen. Case Report: We report the case of a 14-year-old girl who presented with a painless, rapidly growing mass in the left breast, first noticed approximately six months earlier. Clinical examination revealed a mobile lesion about 10 cm in diameter without skin changes, lymphadenopathy, or nipple discharge. Ultrasound and MRI demonstrated a large, well-circumscribed solid tumor (10.4 × 11.2 × 4.2 cm³) displacing normal breast tissue but without infiltration; both were classified as BI-RADS 4. Given the tumor size, diagnostic uncertainty, and potential risk of a non-representative core needle biopsy, a decision was made to proceed with primary radical excision. The mass was completely removed with preservation of the glandular tissue. Histopathology confirmed PASH, described macroscopically as a solid, gray-yellow, encapsulated tumor and microscopically as slit-like spaces lined by spindle cells (CD34+, CD31-). Postoperatively, the breast gradually regained symmetry with the contralateral side, and at 14 months of follow-up, no recurrence was observed. Conclusions: PASH, although benign, may present as a large breast tumor in adolescents and clinically mimic both benign and malignant lesions. Histological evaluation based on an adequately performed biopsy is crucial for accurate diagnosis. Complete excision with capsule preservation is recommended to minimize the risk of recurrence. In adolescents, a watchful waiting approach after surgery may be beneficial, as breast tissue often remodels and regains symmetry spontaneously, reducing the need for reconstructive procedures. This case underscores the importance of individualized diagnostic and therapeutic strategies in managing rare benign breast lesions in pediatric patients.