Successful preimplantation genetic testing for fibrodysplasia ossificans progressiva: a case report.

PURPOSE OF THE STUDY: Fibrodysplasia ossificans progressiva (FOP) is a rare autosomal dominant condition that leads to significant disability and morbidity, characterised by the formation of heterotopic hard tissues within connective tissues. The condition has an incidence of approximately one per two million people worldwide. There is no known single effective treatment available for FOP. We report the world's first case of a healthy infant born following in vitro fertilisation (IVF) and preimplantation genetic testing for monogenic disorder (PGT-M) using Karyomapping for FOP. CASE PRESENTATION: A 30-year-old Caucasian female with FOP presented with her partner seeking IVF with PGT-M to achieve a healthy pregnancy with an embryo unaffected by FOP. METHODS: The couple underwent IVF and PGT-M using Karyomapping as the testing method. A multi-disciplinary team approach was utilised in planning this case, considering the additional risks of oocyte retrieval, pregnancy and childbirth in women with FOP. MAIN FINDINGS: The oocyte retrieval was covered with a 5-day course of prednisolone to reduce the risk of a localised inflammatory reaction, which could result in subsequent heterotopic ossification. This was subsequently weaned down with reducing doses every two days. The patient underwent uncomplicated oocyte retrieval, yielding 12 mature oocytes. Following intracytoplasmic sperm injection (ICSI), ten zygotes having two pro-nuclei were cultured, and six underwent trophoectoderm biopsy and vitrification 5-6 days after retrieval. PGT-M via Karyomapping revealed four out of six (66.7%) of blastocysts were not carriers of the maternal high-risk FOP allele. In total, the patient had three separate embryo transfers. Pregnancy was achieved following the third frozen embryo transfer, which went to 37 weeks' gestation, and delivered by Caesarean section. The baby was born in excellent condition and is unaffected by FOP. CONCLUSION: IVF/ICSI and PGT-M using Karyomapping was successfully implemented to identify embryos carrying the high-risk FOP allele resulting in a healthy livebirth.

Pay Attention to the Osteochondromas in Fibrodysplasia Ossificans Progressiva.

BACKGROUND: Fibrodysplasia ossificans progressiva (FOP) is an extremely rare disease characterized by malformation of the bilateral great toes and progressive heterotopic ossification. The clinical features of FOP occur due to dysfunction of the bone morphogenetic protein (BMP) signaling pathway induced by the mutant activin A type I receptor/activin-like kinase-2 (ACVR1/ALK2) which contributes to the clinical features in FOP. Dysregulation of the BMP signaling pathway causes the development of osteochondroma. Poor awareness of the association between FOP and osteochondromas always results in misdiagnosis and unnecessary invasive operation. CASE PRESENTATION: In this study, we present a case of classical FOP involving osteochondroma. An 18-year-old male adolescent, born with deformity of bilateral big toes, complained multiple masses on his back for 1 year. The mass initially emerged with a tough texture and did not cause pain. It was misdiagnosed as an osteochondroma. After two surgeries, the masses became hard and spread around the entire back region. Meanwhile, extensive heterotopic ossification was observed around the back, neck, hip, knee, ribs, and mandible during follow-up. Osteochondromas were observed around the bilateral knees. No abnormalities were observed in the laboratory blood test results. Whole exome sequencing revealed missense mutation of ACVR1/ALK2 (c.617G > A; p.R206H) in the patient and confirmed the diagnosis of FOP. CONCLUSION: In summary, classical FOP always behaves as a bilateral deformity of the big toes, as well as progressive ectopic ossification and osteochondromas in the distal femur and proximal tibia. An understanding of the association between osteochondromas and FOP aids in diagnosis and avoids unnecessary invasive management in patients.

Disease aggravation following surgery in a rare patient suspected to Fibrodysplasia (Myositis) ossificans progressiva: a case report.

BACKGROUND: Fibrodysplasia ossificans progressiva (FOP) as a rare and heritable disorder with the infrequent genetic transmission of the condition is a catastrophic disorder of heterotopic ossification (HO) and a cause of extraskeletal bone formation in humans. Given the lack of effective treatment for this disease, the important point is to avoid aggravating factors such as bone biopsy, surgery, and intramuscular injection. CASE PRESENTATION: In this report, we present a 52-year-old female patient, Kurdish ethnic, suspected to FOP who had a surgical intervention on the second toe of the right foot, which subsequently, it caused further deterioration of the disease in the person including necrosis and amputation of the distal phalanx of the second toe. CONCLUSIONS: Although, based on our investigation and the available scientific evidence, surgery may a cause for faster progression and worsening of the FOP disorder, but its proof requires further studies.

Patient-specific PEEK implant for treatment of temporal myositis ossificans (five years follow-up): A case report.

Myositis ossificans of the temporalis muscle results in a cosmetic problem both before and after treatment because of the preoperative swelling and the postoperative defect respectively. The authors hypothesized that a patient-specific Polyether-ether ketone implant can be appropriate for immediate obliteration and reconstruction of such defect benefiting from the accuracy of CAD/CAM technology and computer-guided maxillofacial surgery. A Forty-year-old male patient with myositis ossificans affecting the left temporalis muscle was treated with a computer-guided surgical approach, a patient-specific implant was fabricated to obliterate the defect and avoid temporal hollowing using PEEK material. The functional and cosmetic results were satisfactory both immediately and at the 5-year follow-up, except that the skin over the implant was noticed to be stretched after 5 years. Hence, it can be concluded that virtual surgical planning and PEEK patient-specific implants are reliable in the immediate reconstruction of post-surgical temporal hollowing.

Myositis Ossificans with Aneurysmal Bone Cystic Changes at the Thoracic Paraspinal Region: A Case Report.

Myositis ossificans (MO) is a benign heterotopic bone formation in muscle or soft tissue. It is a self-limiting disease that is usually initiated by trauma and often occurs in the extremities of the body. Here we report a rare case of traumatic myositis ossificans caused by unusual trauma (extracorporeal shock wave therapy) at thoracic paraspinal muscles. After a needle biopsy, the lesion increased in size, and the patient's symptoms worsened. Malignant soft tissue tumors such as osteosarcoma should be differentiated, so excision of the mass was performed. The final diagnosis was MO with aneurysmal bone cystic change. This case is a very rare form of MO that showed an unusual cause, location, clinical course, and pathologic result on follow-up. This can be an instructive case for radiologists as it is a common disease entity with unusual manifestations.

[Progressive myositis ossificans: Case report]. / Miositis osificante progresiva: reporte de un caso.

Background: Myositis ossificans progressiva (MOP) is a low prevalence hereditary connective tissue disease (1:2,000,000 habitants). It is characterized by heterotopic ossification with an uncertain behavior that has been exceptionally related to neoplasms. The objective was to know the coexistence of MOP with neoplasms of mesodermal origin, so that they can be considered in the diagnosis of other patients, as well as formulate hypotheses to clarify their association. Clinical case: 27-year-old female with right gluteal and ischitiobial muscle pain that increased with exercise, without remission with analgesics until limiting the mobility of both extremities. A bone series was requested where areas of heterogeneous radiolucency were evidenced in the region of, both, thighs and pelvis in an irregular manner, similar to bone density, which was compatible with the ultrasound and tomographic findings; we concluded that they were images of myositis ossificans of the hip. The patient reported gastric symptoms and an endoscopy was requested, which histopathologically reported diffuse gastric carcinoma with signet ring cells; cabinet images showed an ovarian tumor. Conclusion: MOP is a low prevalence disease, which is why its knowledge and suspicion are essential for the diagnosis. We found little literature that involves the three entities; therefore, their pathophysiology and understanding is limited. Regarding MOP, at this moment there is no curative treatment; however, an accurate diagnosis allows to start rehabilitation in a timely manner with an improvement in the quality of life.

Introducción: la miositis osificante progresiva (MOP) es una enfermedad hereditaria del tejido conectivo de baja prevalencia (1:2,000,000 habitantes). Se caracteriza por osificación heterotópica con un comportamiento incierto que excepcionalmente se ha relacionado con neoplasias. Se buscó conocer la coexistencia de la MOP con neoplasias de origen mesodérmico, para que sean consideradas en el diagnóstico de otros pacientes, así como formular hipótesis para esclarecer su asociación. Caso clínico: mujer de 27 años con dolor de músculo isquitiobial y glúteo derecho que incrementaba con el ejercicio, sin remisión con analgésicos hasta limitar la movilidad de ambas extremidades. Se solicitó una serie ósea donde se evidenciaron zonas de radiolucidez heterogénea en la región de ambos muslos y pelvis de manera irregular, semejante a densidad ósea, que fue compatible con los hallazgos ecográficos y tomográficos; se concluyó que eran imágenes relacionadas con miositis osificante de cadera. La paciente refirió sintomatología gástrica y se solicitó una endoscopía que histopatológicamente reportó carcinoma gástrico difuso con células en anillo de sello; las imágenes de gabinete mostraron tumoración ovárica. Conclusión: la MOP es una patología de baja prevalencia, por lo que su conocimiento y sospecha son fundamentales para el diagnóstico. Hay poca literatura que involucre a las tres entidades; por ende, su fisiopatología y comprensión es limitada. En cuanto a la MOP, aún no hay un tratamiento curativo; sin embargo, el diagnóstico certero permite iniciar rehabilitación de manera oportuna con mejoría de la calidad de vida.

Dental management of a 26-year-old female with fibrodysplasia ossificans progressiva: A case report.

PURPOSE: The purpose of the report is to present a rare case of clinical management of a 26-year-old patient with fibrodysplasia ossificans progressiva (FOP), and discuss treatment options and possible outcomes. SUMMARY: FOP is a rare autosomal dominant genetic disorder of the connective tissue that affects one in two million people. It is characterized by multiple areas of progressive heterotopic endochondral ossifications. The symptoms typically begin with painful soft tissue swellings in the patient's first decade, which frequently occur after minor trauma, but may also happen spontaneously. The soft tissue swellings eventually form hard bony masses that cause joint limitations, growth defects, skeletal deformities, and chronic pain. The results are severely limiting to the activities of daily living and overall quality of life with the average life expectancy being 40 years of age. Medical and dental treatment, including the use of general anesthesia, may be complicated by increased risk of ossification of the soft tissues in the airway and lungs. The following case report focuses on a 26-year-old Caucasian female, with FOP. The patient presented to the Erie County Medical Center Dental clinic in Spring 2019 with generalized dental pain. She reported a history of multiple dental infections over many years which were periodically treated with antibiotics. A thorough intraoral exam and radiographs were not able to be completed upon initial presentation due to severe trismus and mobility limitations. The patient was a wheelchair user, verbal, and maintained a completely liquid diet by mouth. The patient also had a medical history significant for dysphagia and aspiration. After a substantial pre-operative optimization process, the patient was brought to the operating room for full mouth dental extractions. At the 2-week follow-up from surgery the patient showed excellent healing. CONCLUSION: While there are greater potential risks with placing a patient with FOP patient under general anesthesia, proper management of dental disease can relieve the patient from recurrent infections and discomfort.

A case of Fibrodysplasia Ossificans Progressiva associated with a novel variant of the ACVR1 gene.

BACKGROUND: Fibrodysplasia Ossificans Progressiva (FOP) is a rare autosomal dominant disease characterized by congenital malformation of the great toes and progressive heterotopic ossification of soft tissues leading to cumulative disability. The genetic cause of FOP are mutations in the ACVR1 gene that encodes a type I receptor of Bone Morphogenetic Proteins. The most recurrent mutation in FOP patients is R206H affecting the Glycine-Serine rich domain and causing the hyper-activation of the receptor and the responsivity to the non-canonical ligand, Activin A. In the present study, we described a 3-years old child with early and highly suggestive clinical features of FOP who was found negative for the recurrent p.R206H substitution. METHODS: Molecular screening of the whole ACVR1 coding sequence and functional characterization in transfection-based assays. RESULTS AND CONCLUSIONS: We identified a novel, de novo variant in the fifth ACVR1 coding exon (NM_001111067.4:c.772A>T; NP_001104537.1:p.(R258W)). This substitution, never reported in association with FOP, affects a conserved arginine residue in the kinase domain of the protein. In silico analysis predicted the pathogenicity of this substitution, demonstrated by in vitro assays showing that the p.R258W ACVR1 mutated receptor acquires the ability to transduce the aberrant Activin A-mediated signaling, as observed for the gene variants associated with FOP.

Fibrodysplasia ossificans progressiva (FOP) presenting as a rapidly growing non-calcified neck mass.

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare autosomal dominant inherited disorder leading to mature ossification within soft tissues. We report a 62-year-old female with a 3-week history of a rapidly enlarging left neck mass with no associated symptoms. A neck CT showed a ~10 cm solid-appearing non-calcified left neck mass that markedly decreased in size on a one-month follow-up neck MRI, but with new extensive edema/intense enhancement in floor of the mouth. Prior radiographs documented hallux valgus and heterotopic ossification of the psoas/paraspinal muscles and shoulder girdle. In this case of FOP, no intervention was implemented and the symptoms improved over time and thus paralleled other such cases for flare-ups. Clinicians should be aware of this rare entity, as it is frequently misdiagnosed as cancer or other benign entities such as infection, resulting in biopsies that can often hasten disease progression.

Post-COVID-19 exacerbation of fibrodysplasia ossificans progressiva with multiple flare-ups and extensive heterotopic ossification in a 45-year-old female patient.

Fibrodyplasia ossificans progressiva (FOP) is a rare hereditary disease, which has a variable course characterized by occasional flare-ups of heterotopic ossification (HO) in soft tissues that are followed by swelling, stiffness, pain and warmth. Here, we report for the first time a case of a 45-year-old female patient with known FOP recovering from COVID-19 with disease progression potentially linked with the viral illness. In December 2020 the patient contracted a mild form of COVID-19 infection without need for hospital admission. Since January 2021, the patient felt unwell, with occasional abdominal pain which progressively intensified. In March 2021 she presented with new onset of HO, complaining of pain, swelling and thickening sensation in the lower abdomen and left part of the neck. Computerized tomography (CT) and cytokine analysis were performed. CT scan revealed new heterotopic bone formation in multiple soft tissue areas of the neck indicating clear radiological progression. Radiotherapy, which has proven to be an efficient tool to control HO in this patient, was not able to halt HO formation after COVID-19 infection. Cytokine analysis of a plasma sample obtained during a flare-up after COVID-19 infection showed a significantly elevated pro-inflammatory cytokines compared to a flare-up panel prior to infection. Of the 23 analyzed levels of cytokines, a staggering number of 21 were above normal levels. This case is the first confirmation of uncontrolled post-COVID-19 effects in a FOP patient, which manifested with flare-ups followed by progressive HO, possibly caused by a thus far, never described form of post-COVID syndrome.

Clinicopathological and molecular characterisation of USP6-rearranged soft tissue neoplasms: the evidence of genetic relatedness indicates an expanding family with variable bone-forming capacity.

AIMS: USP6 rearrangement underpins self-limiting fibroblastic/myofibroblastic neoplasms, including nodular fasciitis (NF), myositis ossificans (MO), aneurysmal bone cyst (ABC), and related variants. The aim of this study was to characterise UPS6 and fusion partners in order to delineate the clinicopathological, genetic and bone-forming features in such lesions of soft tissue (ST). METHODS AND RESULTS: Break-apart fluorescence in-situ hybridisation (FISH) validated USP6 rearrangement in 31 of 35 NF [comprising three of three fasciitis ossificans (FO) cases, seven of eight cellular variant of fibroma of tendon sheath (C-FTS), four of six MO, three of three ST-ABC, and two of two fibro-osseous pseudotumours of digits (FOPD)]. As determined with FISH and reverse transcription polymerase chain reaction, MYH9-USP6 was the commonest fusion in four C-FTS and 20 NF, including one intravascular case and two infantile (one retroperitoneal) cases. The presence of MYH9-USP6 confirmed the diagnosis of two NFs> 50 mm with prominent ischaemic necrosis. COL1A1-USP6 was predominant in ossifying lesions, including all FO, MO, ST-ABC and FOPD with identified partner genes, and was also present in non-ossifying head and neck NF (HN-NF) and C-FTS in two cases each. A cervical NF of a 14-month-old girl harboured the novel COL1A2-USP6. Ossifying lesions showed considerable genetic and morphological overlaps. Sharing COL1A1-USP6, FO and FOPD showed similar central or haphazard bone matrix deposition. Besides zonation of outward bone maturation, four COL1A1-USP6-positive MO had incipient to sieve-like pseudocysts reminiscent of ST-ABC. CONCLUSION: MYH9-USP6 is present in some C-FTS and most NF, including rare variants, but is unrelated to bone formation. All bone-forming USP6-rearranged lesions adopt COL1A1 as the 5' partner, indicating close genetic kinships. However, COL1A1/COL1A2 also contributes to the pathogenesis of minor subsets of non-ossifying USP6-rearranged HN-NF and C-FTS.

A Clinical Perspective on Advanced Developments in Bone Biopsy Assessment in Rare Bone Disorders.

Introduction: Bone biopsies have been obtained for many centuries and are one of the oldest known medical procedures in history. Despite the introduction of new noninvasive radiographic imaging techniques and genetic analyses, bone biopsies are still valuable in the diagnosis of bone diseases. Advanced techniques for the assessment of bone quality in bone biopsies, which have emerged during the last decades, allows in-depth tissue analyses beyond structural changes visible in bone histology. In this review, we give an overview of the application and advantages of the advanced techniques for the analysis of bone biopsies in the clinical setting of various rare metabolic bone diseases. Method: A systematic literature search on rare metabolic bone diseases and analyzing techniques of bone biopsies was performed in PubMed up to 2019 week 34. Results: Advanced techniques for the analysis of bone biopsies were described for rare metabolic bone disorders including Paget's disease of bone, osteogenesis imperfecta, fibrous dysplasia, Fibrodysplasia ossificans progressiva, PLS3 X-linked osteoporosis, Loeys-Diets syndrome, osteopetrosis, Erdheim-Chester disease, and Cherubism. A variety of advanced available analytical techniques were identified that may help to provide additional detail on cellular, structural, and compositional characteristics in rare bone diseases complementing classical histopathology. Discussion: To date, these techniques have only been used in research and not in daily clinical practice. Clinical application of bone quality assessment techniques depends upon several aspects such as availability of the technique in hospitals, the existence of reference data, and a cooperative network of researchers and clinicians. The evaluation of rare metabolic bone disorders requires a repertoire of different methods, owing to their distinct bone tissue characteristics. The broader use of bone material obtained from biopsies could provide much more information about pathophysiology or treatment options and establish bone biopsies as a valuable tool in rare metabolic bone diseases.

Fibrodisplasia osificante progresiva en pediatría: a propósito de un caso clínico / Fibrodysplasia ossificans progressiva in pediatrics: a case report

Introducción: La Fibrodisplasia osificante progresiva es una enfermedad congénita autosómica dominante poco frecuente, caracterizada por malformaciones esqueléticas y osificación heterotópica progresiva e invalidante. Caso clínico: Niño de 11 años consulta por múltiples lesiones osificadas en tronco y región cervical con importante limitación en su movilidad. En el examen físico destaca un ortejo mayor corto. Estudio genético muestra mutación del gen ACVR1. Recibe tratamiento con periodos cortos de corticosteroides posterior a traumas y previo a procedimientos, asociado a un manejo multidisciplinario. Revisión de la literatura: A la fecha el principal tratamiento es la prevención de los brotes de osificación y el uso de corticosteroides o antiinflamatorios cuando los brotes ya se iniciaron. Están en curso ensayos clínicos con bifosfonatos y anticuerpos anti-activina A. Conclusión: En la actualidad no existe un tratamiento específico, sin embargo, un diagnóstico precoz, la prevención de brotes y nuevas terapias podrían mejorar el pronóstico de los pacientes.

ntroduction: Fibrodysplasia ossificans progressiva is a rare autosomal dominant congenital disease characterized by skeletal malformations and progressive disabling heterotopic ossification. Clinical case: An 11-year-old boy consulted with multiple ossified lesions in the trunk and cervical regions associated with significant limitation in mobility. On physical examination, the big toe is short. Genetic study shows ACVR1 gene mutation. He received treatment with short corticosteroid periods after traumas and prior to clinical procedures, as well as a multidisciplinary management.Literature review: To date the main treatment is the prevention of ossification flare-ups and the use of corticosteroids or anti-inflammatories when they have already started. Clinical trials are ongoing with bisphosphonates and anti-activin A antibodies.Conclusion: There is currently no specific treatment, however, early diagnosis, prevention of flare-ups and new therapies could improve the prognosis of patients.

Myositis ossificans traumatica of the piriformis muscle: a rare mature case in an adult African male.

Myositis ossificans traumatica (MOT) is a common form of heterotopic ossification associated to trauma. Rare mature manifestations and topographically atypical presentations of MOT are often misdiagnosed as osteosarcoma. This case study discusses a rare, mature case of MOT of the piriformis muscle, potentially clinically associated with piriformis syndrome. The ossification was observed on a dry sacral bone of an adult skeleton belonging to a South African male during routine inventory of the Raymond A. Dart Collection of Human Skeletons, the University of the Witwatersrand, Johannesburg. The MOT was located on the anterior aspect of the sacrum at a site corresponding to the upper portion of the origin of the muscle and extended laterally towards the greater trochanter, beyond the greater sciatic notch. It was cylindrical in shape and measured approximately 52.70 mm in length and 12.10 mm in diameter. Micro-focus CT revealed an extensive and mature bony development of the piriformis muscle with distinct outer cortical and inner trabecular bone. In addition, the skeleton showed widespread healed skeletal trauma, suggesting a history of trauma. The MOT was completely fused to the sacral bone excluding the possibility of congenital anomalies. Information on the MOT of the piriformis muscle is vital to clinicians and radiographers to aid in successful diagnosis and management of the piriformis syndrome and sciatica in the gluteal region. This case also provides a rare example to biological anthropologists, paleoanthropologists and bioarchaeologists of the representation of pathologies like these on a dry bone sample.

Differential Vascularity in Genetic and Nonhereditary Heterotopic Ossification.

Introduction. Nonhereditary heterotopic ossification (NHO) is a common complication of trauma. Progressive osseous heteroplasia (POH) and fibrodysplasia ossificans progressiva (FOP) are rare genetic causes of heterotopic bone. In this article, we detail the vascular patterning associated with genetic versus NHO. Methods. Vascular histomorphometric analysis was performed on patient samples from POH, FOP, and NHO. Endpoints for analysis included blood vessel (BV) number, area, density, size, and wall thickness. Results. Results demonstrated conserved temporal dynamic changes in vascularity across all heterotopic ossification lesions. Immature areas had the highest BV number, while the more mature foci had the highest BV area. Most vascular parameters were significantly increased in genetic as compared with NHO. Discussion. In sum, both genetic and NHO show temporospatial variation in vascularity. These findings suggest that angiogenic pathways are potential therapeutic targets in both genetic and nonhereditary forms of heterotopic ossification.

Non-traumatic myositis ossificans of the thigh. A case report.

INTRODUCTION: Myositis ossificans (MO) is an ectopic ossification characterized by an appearance of bone formation predominantly in muscle tissue. Trauma is the most common etiological factor, observed in almost 60-75% of cases, whereas a non-traumatic MO is rarely described in the literature. A diagnosis is based on clinical and radiological findings. PRESENTATION OF CASE: A 75-year old female patient has been admitted to our clinic with a localized swelling of the posterior femoral compartment, presented on magnetic resonance as a calcification in the biceps femoris muscle. Laboratory test results were within the normal range. Surgical procedure consisted of excision of the tumor mass with primary wound reconstruction and drainage. The post-operative period was uneventful, and the patient was discharged from hospital on the seventh postoperative day. The pathohistology findings have shown the MO. DISCUSSION: A non-traumatic MO is scarcely described in the literature. A chronic microtrauma, tissue ischaemia and inflammation are listed as causal mechanisms of a non-traumatic MO. MO non-traumatica occurs more often in patients with a parallel, subdural or epidural haemorrhage and a hip surgery. Our case did not present any family history, trauma or associated anomalies of hands or fingers. CONCLUSION: Myositis ossificans should be considered as the differential diagnosis of all soft tissue tumor masses, even if known risk factors are not present in the anamnesis. Surgery is a reasonable therapeutic strategy in the presence of a tumor mass in soft tissues, and definite diagnosis can be set only based on pathohistological findings. KEY WORDS: Ectopic ossification, Non traumatic myositis, Surgery.

Myositis ossificans mimicking metaplastic breast cancer on core needle biopsy.

Myositis ossificans (MO) is an uncommon myofibroblastic proliferation that may closely mimic sarcoma. A 33-year old woman presented with a 2-cm breast mass. A core needle biopsy showed highly cellular spindle cell proliferations with atypia and high proliferation activity. Focal areas of immature osteoid-like matrix were seen. After immunohistochemical analysis, a diagnosis of metaplastic breast cancer was made. Because of the proximity of the tumor to the rib, resection of the tumor including partial resection of the rib was carried out. Complete examination of the excised lesion allowed the correct diagnosis of MO. Only the resection specimens contained a predominance of mature organoid bone tissue admixed with variably cellular myofibroblastic proliferations with the typical zonal pattern, characteristic of MO. The diagnosis of MO was not possible on the initially performed core needle biopsy because biopsy material reflected only the central proliferative portion of the lesion showing increased pleomorphism and early osteoid formation. This case highlights the pitfall related to this unusual presentation of a benign lesion and points to the necessity to include MO in the differential diagnosis of triple-negative metaplastic breast cancer.