Recurrent Desmoid-Type Fibromatosis of the Breast in a Young Woman With a Monoallelic MUTYH Germline Variant

Desmoid-type fibromatosis of the breast is an uncommon, low-grade mesenchymal neoplasm with benign histologic features, characterized by locally aggressive growth and a notable tendency for local recurrence. Clinical management is challenging owing to frequent positive surgical margins, a propensity for recurrence, and the absence of standardized treatment guidelines. We report the case of a 34-year-old woman who underwent mastectomy for recurrent breast desmoid-type fibromatosis, in whom a heterozygous germline MUTYH (MutY DNA glycosylase) variant was identified through hereditary cancer panel testing. This case highlights the potential value of comprehensive pathologic assessment and selective germline genetic testing in patients with recurrent breast fibromatosis, which may offer further insight into tumor biology and inform individualized management strategies.

Aggressive Fibromatosis (AF) is a rare mesenchymal tumor characterized by nuclear β-catenin positivity. Its exact etiology remains unclear but is thought to be associated with hormonal factors, trauma, or prior surgery. Clinically, AF is uncommon and demonstrates nonspecific imaging features, frequently complicating preoperative diagnosis. This is particularly true for intra-abdominal AF presenting with atypical features, which can be easily mistaken for other abdominal space-occupying lesions. Herein, we report two rare cases of primary intestinal AF, one of which was complicated by tumor rupture and subsequent intra-abdominal abscess formation. Through an integrated analysis of clinical presentation, imaging findings, and pathological results, this report discusses the diagnostic considerations and management strategies for AF.

Introduction: Desmoid fibromatosis (DF) is a rare, locally invasive, and typically non-metastatic neoplasm. Its pathophysiology is poorly understood, and the subtle clinical presentation makes diagnosis challenging. A multidisciplinary approach is necessary to achieve a definitive diagnosis and identify the most effective therapeutic strategy. Because of its heterogeneous presentation and unpredictable behavior, DF cannot be managed through a standardized protocol, and diagnostic and therapeutic decisions must instead be tailored to the individual patient, consistent with a personalized-medicine approach. We present an unusual case in which we aim to evaluate the diagnostic procedures and treatments used and determine whether they align with the recent literature. Materials and Methods: A case report. A 27-year-old man presented with fever and worsening abdominal pain, without clinical signs of intestinal obstruction. He had undergone a sleeve gastrectomy five years earlier. A computed tomography (CT) scan revealed an intra-abdominal mass in the mesohypogastric region, likely originating from the mesentery of the small intestine. The patient underwent a right hemicolectomy extended to the terminal ileum. Histopathological examination and immunohistochemistry confirmed the diagnosis of DF. The patient was discharged on the 5th postoperative day (POD) in good general clinical condition. To date, there are no signs of recurrence. Conclusions: The multidisciplinary approach is essential for managing DF and R0 surgical resection remains the gold standard. The diagnostic and therapeutic pathway followed in our patient appears consistent with the recent literature. This case illustrates how individualized clinical reasoning can be applied even to a rare, heterogeneous neoplasm for which no standardized protocol exists. Furthermore, an established post-surgical management protocol for DF has not yet been developed. Additionally, we observed a possible, hypothesis-generating association between bariatric surgery and the subsequent onset of an intra-abdominal desmoid tumor; given the rarity of desmoid fibromatosis relative to the high volume of bariatric procedures performed worldwide, this observation should not be interpreted as a confirmed correlation, and we conducted a literature review to explore it as a hypothesis. Numerous studies are needed on this matter, but we hope that this case can provide a small starting point for subsequent studies.

Desmoid tumors (DTs) are rare fibroblastic neoplasms driven by altered Wnt signaling pathways, through activating mutations in β-catenin (CTNNB1) or loss of repressive APC. DTs are considered as intermediate neoplasms that can be locally aggressive, with potential for significant medical complications that can threaten life and limb, as well as impact on patient function, quality of life, and emotional well-being. Historically, DTs were treated with similar paradigms as soft tissue sarcomas, with complete surgical resection the priority despite frequent postoperative recurrences, or use of radiation or cytotoxic chemotherapies for refractory/recurrent cases. Today, improved understanding of DT biology and natural history, along with the development of molecularly targeted therapies, has greatly changed the recommended approach to DT management. In this review, we highlight the role of active surveillance for initial management of most DTs, recognizing the potential for tumor stability or spontaneous regression. In the case of highly symptomatic or progressive tumors, we review the spectrum of treatment options, including surgery for select cases, systemic therapies such as novel gamma secretase inhibitors and tyrosine kinase inhibitors, and emerging local treatment options including cryoablation and high-intensity focused ultrasound. Through a multidisciplinary approach and careful assessment of the individual patient’s DT biology and symptomatic impacts, the optimal treatment strategy can be selected to minimize unnecessary morbidity and toxicity and to improve outcomes and quality of life for this unique patient population.

Objective: To investigate the value of 18F-FDG PET/CT in assessing the local aggressiveness of desmoid-type fibromatosis (DF) and in predicting prognosis of DF.

Methods: We retrospectively analyzed 18F-FDG PET/CT of DF lesions in participants. Clinical data and 18F-FDG PET/CT imaging features were collected and analyzed. The diagnostic performance of 18F-FDG PET/CT versus contrast-enhanced MRI (CE-MRI) for assessing peritumoral invasion was compared using reference of pathology. Lesions were followed up to record progressive disease (PD) and postoperative recurrence (POR), and event-free survival (EFS) was determined. Univariate and multivariate Cox regression analyses were performed to identify independent predictors of PD or POR.

Results: Fifty-five lesions from 44 participants were included. ¹⁸F-FDG PET/CT showed higher accuracy and sensitivity than CE-MRI for assessing peritumoral invasion, with no statistically significant differences in paired comparisons. Notably, pathology in one case demonstrated tumor invasion of the lymph node capsules. Furthermore, DF lesions with PD or POR had significantly higher maximum standardized uptake value (SUVmax) and target-to-background ratio (TBR). SUVmax, TBR and irregular lesion morphology were identified as independent predictors of PD or POR. The AUC for SUVmax was 0.79 (95% CI: 0.64-0.95), with sensitivity, specificity, and overall accuracy of 78.6% (11/14), 82.9% (34/41), and 81.8% (45/55), respectively. Kaplan-Meier survival analysis revealed that SUVmax> 5.0 was associated with significantly shorter EFS (692.4 [427.5-957.3] days vs. 2419.9 [1989.5-2850.3] days).

Conclusion: 18F-FDG PET/CT showed numerically higher sensitivity and accuracy than CE-MRI for assessing peritumoral invasion of DF lesions, though with lower specificity. SUVmax, TBR, and lesion morphology were independent predictors of PD or POR.

We present the case of a 35-year-old woman with an abdominal wall mass initially diagnosed radiologically as a schwannoma. Histopathology revealed desmoid fibromatosis through β-catenin positivity, despite no trauma or surgical history. Complete excision with negative margins was curative, highlighting immunohistochemistry’s diagnostic value and surgical efficacy.