The oncocytoma is a tumor composed of oncocytes – epithelial cells characterized by an excess of mitochondria – which materialize in an abundant, granular, acidophilic cytoplasm. This tumor is often benign but not infrequently borderline or even malignant.
What is the typology of the oncocytoma?
The oncocytoma can develop in several organs, but is typically found in the kidney, salivary or thyroid glands.
Oncocytoma of the salivary glands most commonly occurs as a well-circumscribed tumor. It represents less than 1% of the total number of tumors developed at this level and is found predominantly in women of advanced age. They can often be bilateral, and clinically present as a hard, slowly evolving and painless tumor mass.
The thyroid oncocytoma may be benign (adenoma) or malignant (carcinoma). The adenoma is a solid encapsulated tumor and the minimally invasive oncocytic carcinoma has a similar appearance. In contrast, extensive invasive carcinoma is multifocal and has vascular extension.
From a cytological point of view, there is no difference between oncocytic adenomas and carcinomas, the only diagnostic criterion of malignancy being the identification of transcapsular or vascular invasion.
Renal oncocytoma is a benign increase in renal parenchyma, generally asymptomatic and often accidentally discovered, during imaging investigations performed for other diseases. Although it can occur in people of all ages, renal oncocytoma is the preserve of middle-aged and older men (over 60 years of age). If a causal element cannot be identified for the single oncocytoma, multiple or bilateral oncocytomas are most often part of genetic syndromes, such as tuberous sclerosis complex.
What are the symptoms?
In the case of renal oncocytoma, most people do not show signs or symptoms. In fact, these tumors are often discovered by accident while a person undergoes a diagnostic image for other conditions. In approximately one third of the cases, people with renal oncocytoma will present with abdominal or flank pain, urine blood and / or an abdominal mass.
What are the causes of this tumor?
The exact underlying cause of most renal oncocytomas is unknown. However, researchers suspect that acquired (and not present at birth) changes in mitochondrial DNA may play a role in the development of some of these tumors.
Renal oncocytomas sometimes occur in people with certain genetic syndromes, such as tuberous sclerosis complex and Birt-Hogg-Dube syndrome. In these cases, the affected people often have multiple and bilateral oncocytomas (affecting both kidneys) and may also have family members with these tumors. When renal oncocytomas are part of a genetic syndrome, they are caused by changes (mutations) in a specific gene. Tuberous sclerosis complex is caused by mutations of the TSC1 or TSC2 gene, while Birt-Hogg-Dube syndrome is caused by mutations of the FLCN gene. Most renal oncocytomas are not inherited. Usually, they occur sporadically in people without a family history of tumors. However, in rare cases, these can occur in people with certain genetic syndromes, such as tuberotic sclerosis complex and Birt-Hogg-Dube syndrome.
Evolution and forecast
The long-term prognosis in patients with sporadic oncocytoma is generally good. These tumors are almost always benign and metastasis is very rare. After surgical resection, recurrence is unlikely.
When we talk about renal oncocytoma as part of a genetic syndrome, the prognosis is variable. The lifespan of the affected persons is not usually affected by the tumor. When a renal oncocytoma is part of a genetic syndrome such as tuberotic sclerosis complex and Birt-Hogg-Dube syndrome, the prognosis varies depending on the other associated signs and symptoms.
What is the treatment for oncocytoma?
Although many benign tumors do not require treatment unless they are symptomatic, it is very difficult to differentiate an oncocytoma from a renal carcinoma. In these conditions, the majority of patients undergo surgery for both diagnostic and therapeutic purposes. If the suspicion for an oncocytoma is raised, a limited surgical procedure, such as partial nephrectomy, can be performed. In the absence of suspicion, almost always total nephrectomy is resorted to.