Secondary ABC does not harbor a USP6 alteration, although the detection of a genetic aberration characteristic of the primary tumor, such as GNAS R201 alterations involving R201H (~57 %), R201C (~38 %), and Q227L (~5 %) in fibrous dysplasia [9] (Fig. 1), a GRM1 alteration in chondromyxoid fibroma [10], and H3.3 alterations in giant cell tumor of bone and chondroblastoma [11], can help in reaching a diagnosis. The gene discussed is USP6; the disease is chondromyxoid fibroma.