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.