Direct bone invasion in squamous carcinomas of the head and neck: pathological and clinical implications.

Direct bone invasion by tumour--an uncommon event at most sites--has been demonstrated in 18 out of 150 consecutive major surgical specimens from patients with squamous carcinomas of the head and neck. Intra-oral carcinomas invading the jaw(s) comprise the single commonest group. The tumour gains access to bone by direct spread or along perineural spaces: infiltration of periosteal lymphatics was rare. The morphological phases of bone invasion are described, the main feature being bone destruction by osteoclasts in front of the advancing tumour; tumour cells do not directly impinge on the bone surface until the late stages of invasion. Osteoblastic activity is less marked. Evidence that osteoclasts are directly stimulated by local tumour is discussed. The clinical implications relate to the possible uses of scintigraphy and the need to ensure adequate bone resections in operable lesions: the tumours sometimes infiltrate laterally beneath apparently intact bone cortex (cf. submucosal spread), and the normal tissue planes at the bone-soft tissue interface are usually distorted by previous radiotherapy.