**3.3 Other risk factors**

Association with different bone dysplasias has also been documented: fibrous dysplasia, Paget's dysplasia, and enchondromatosis [11].


Additionally, HNOS has also been associated with trauma, bone infarcts, and chronic osteomyelitis [13].

Finally, one of the most strongly associated factors is a history of previous radiotherapy. In fact, Patel et al. [15] reported on 44 patients treated at Memorial Sloan-Kettering Cancer Center between 1981 and 1998: six patients (15%) had a history of previous radiotherapy. Different authors describe that this would be mainly for patients who received radiotherapy for leukemia or lymphoma, but no correlation has been found with respect to low-dose radiation received for diagnostic medical tests [13]. In a cohort study from Massachusetts general hospital [16], with 47 patients, prior radiation to the head or neck was documented in 27% of subjects and was statistically associated with decreased overall survival on univariate analysis (p = .01).

In parallel, it is important to consider the epidemiology of the place where we are observing the OS cases. For example, in a Chinese series reported by Luo et al. [17] in 2019, with 37 patients with HNOS, 43% of them had a history of previous radiotherapy for Nasopharyngeal Ca, given that the latter is an endemic disease in that country.
