Discussion:
Mammary myofibroblastomas, in contrast to their MTEM counterparts, are well-circumscribed tumors composed of spindle cells with myofibroblasts, hyalinized collagenous stroma, and adipose tissue.1They can be distinguished from other stromal tumors via SMA, desmin, and CD34 immunohistochemical staining. Outside the breast, myofibroblastomas are exquisitely rare, particularly in the head and neck region. Previously described cases include the suprasellar, zygomatic arch, and orbital bone regions as well as the frontal lobe meninges.4-8 These cases generally report remission and resolution of symptoms following surgical excision of the MTEM. Metastasis or malignant transformation of MTEM has not been reported in literature.9
Ionizing radiation is considered a weak carcinogen, at least in comparison to some cytostatic drugs.10Radiation-induced neoplasms in the head and neck, while rare, can be aggressive, with estimated 5-year survival rates as low as 10-30%.11 The risk of malignancy increases with time following radiation therapy.10 The etiology of neoplastic growth after radiation exposure is still unclear but thought to be due to ionizing DNA damage. Another mechanism of neoplasm formation is inherited loss of heterozygosity with subsequent environmental insults, resulting in complete knock-out of tumor suppressor genes leading to malignant transformation.12 In this patient with a germlineRb mutation, the addition of radiation exposure in childhood carried a significant risk for the development of future malignancies.
The diagnosis of radiation induced sarcomas was established with the Cahan criteria in 1948. Criterion includes developing a sarcoma type tumor in the field of previous radiation treatment with a minimum latency of five years. The tumor must also be histologically distinct from the initial primary tumor.13 While this case satisfies the Cahan criteria, final tissue pathology revealed a much rarer neoplasm of the head and neck and implies a similar connection between myofibroblastomas and external beam radiation exposure.
Radiation-induced myofibroblastomas have been reported in the literature, most commonly concerning the breast.14-15An instance of radiation-induced, low-grade myofibroblastic sarcoma in the maxillary sinus was reported with a patient receiving radiotherapy for nasopharyngeal carcinoma, with the median radiation dose at the cancer site being 66 Gy during previous radiotherapy.16 The reported latency in this case was approximately 60 years, which is a larger time duration when compared with reported solid tumor induction times10 and for the case of reported myofibroblastic sarcoma in the maxillary sinus found in literature.16
General management of radiation-induced neoplasms consists of surgery with wide local resection.17 This is generally advised, as many radiation-induced head and neck neoplasms are aggressive and show bone destruction and local invasion on imaging.16 The reported benign myofibroblastoma lesion in this case was not locally invasive and therefore did not require extensive surgical intervention. Additional radiation therapy and/or chemotherapy have both been suggested but have not been shown to increase overall survival.18 This was also thought to be relatively contraindicated in our patient given his presumed germline retinoblastoma mutation. As such our patient underwent partial maxillectomy and total ethmoidectomy, which was thought to be the most appropriate course of action for this rare but benign lesion.