C

Extension of tumour beyond the sinonasal cavities

Proposed sources of origin of olfactory neuroblastoma include Jacobson's vomero-nasal organ, the sphenopalatine ganglion, the ectodermal olfactory placode, Loci's ganglion, autonomic ganglia in the nasal mucosa, and the olfactory epithelium. While a neuronal - neural crest origin is supported by the presence of neurofilaments in olfactory neuroblastoma {2634}, until recently {335}, few arguments linked olfactory neuroblas-toma directly to the olfactory epithelium. The olfactory neuroepithelium is a unique neurosensory organ because olfactory neurons are continuously replaced throughout adult life by new ones {941,942}. Three types of cells are classically recognized in the olfactory epithelium: the basal cells, located against the basement membrane, the olfactory neu-rosensory cells, and the sustentacular supporting cells, the processes of which extend on the luminal surface. The globose basal cells constitute a stem cell compartment, which confers to this tissue its peculiar ability to regenerate not only physiologically but also when injured by trauma or environmental insults {1631,2690}. The globose basal cells express {1747} neural cell adhesion molecule (NCAM) {513} and mammalian homologue of Drosophila achaete-scute (MASH) gene {958}. These progenitor cells differentiate into olfactory neurosen-sory cells, which exhibit a progressive maturation from the basal membrane to the epithelial surface {1631,1884}. Each layer can be characterized by specific olfactory- and neuron specific markers. Immature olfactory cells express {1631,2690} GAP43, a 24 kD membrane-associated protein kinase C involved in polyphosphoinositide turnover {197}. As these cells mature, they send axons to the olfactory bulb and migrate towards the surface, they express olfactory marker protein (OMP) {1630} and NCAM, but not GAP43 {1631,1884,2690}. Recently, olfactory neuroblastomas were found to express HASH, the human homologue of the MASH gene {335}, while staining negative for OMP. So far, HASH has only been demonstrated in medullary thyroid carcinoma and certain small cell lung carcinoma {111}. Further indirect evidence that olfactory neurob-lastoma originates from olfactory stem cells can be derived from transgenic mice in which, the SV40T oncogene was inserted under the OMP gene promoter region {2307}: these mice did not develop olfactory neuroblastoma but adrenal and sympathetic ganglia neuroblastoma. Therefore, the currently available evidence links olfactory neuroblastoma with the basal progenitor cells of the olfactory epithelium.

Prognosis and predictive factors

Complete surgical eradication (craniofacial resection that includes removal of the cribriform plate) followed by full course radiotherapy is the treatment of choice {625,626,1777}. Limited success using chemotherapeutic modalities have been achieved for advanced unresectable tumours and/or for disseminated disease {2705}. High-dose chemotherapy, including platinum-based protocols and autologous bone marrow transplantation have resulted in long-term survival {634,1919,2064}. The overall 5-, 10- and 15-year survival rates have been reported to be 78%, 71% and 68%, respectively {634}. Initial multimodality therapy is associated with 5-year survival of 80% for low-grade tumours and 40% for high-grade tumours {1777}. The majority of the recurrences occur within the first two years {625}. The most frequent recurrence is local, with rates around 30%. Prognosis has traditionally been correlated to clinical staging with 5-year survival of 75-91%, 68-71% and 4147% for Stage A, B and C tumours, respectively {663,1243}. More recently, complete tumour resection was found to be of more prognostic importance than clinical staging {1740}. Other factors purportedly implicated in prognosis include histologic grading, proliferation rate and ploidy. Histologically lower grade tumours (Grades I and II) have been reported to have a better 5-year survival than highergrade tumours (Grades III, IV) {1159}. High proliferation indices and high rate of ploidy/aneuploidy have been correlated with Increased morbidity (I.e., tumour recurrence, metastasis) and mortality (i.e., decreased survival) {2560,2682}. The majority of tumours behave as locally aggressive lesions mainly involving adjacent structures (orbit and cranial cavity). Local recurrence and distant metastasis may occur years following the initial diagnosis. Approximately 15-70% of patients will experience local recurrence, 10-25% will have cervical lymph node metastasis, and approximately 1060% will experience distant metastasis {131,663}. The more common sites of metastases include lymph nodes, lungs, and bone. All histologic grades have the capacity to metastasize.

Melanotic neuroectodermal tumour of infancy

Definition

Melanotic neuroectodermal tumour of infancy (MNTI) is a rare neoplasm of infants with a biphasic population of neuroblasts cells and pigmented epithelial cells.

ICD-O code 9363/0

[if benign]

Synonyms

Melanotic progonoma, retinal anlage tumour, melanotic ameloblastoma

Epidemiology

The tumour is very rare. It characteristically occurs in infants, with 80% of cases <6 months of age and 95% <1 year of age, with a 2:1 female predominance {1269}.

Localization

More than 85% of patients have a mass involving craniofacial sites: maxilla (70%), mandible (10%), skull (10%), neu-rocranial dura or brain (1%). Occasionally other sites, such as the epi-

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