Differentiation of Oncocytoma From Chromophobe RCC
Differentiation of Oncocytoma From Chromophobe RCC
Standard treatment of renal neoplasms remains surgical resection, and nephrectomy for localised renal cell carcinoma (RCC) still has the best chance of cure with excellent long-term results. For smaller renal masses, especially stage T1a tumours less than 4 cm, nephron-sparing surgery is often employed. However, small incidentally detected renal masses pose an important diagnostic dilemma as a proportion of them may be benign and could be managed conservatively. Renal oncocytoma is one such lesion that may pose little risk to a patient if managed with routine surveillance rather than surgery. Additionally, lower-risk RCC, such as small chromophobe RCC, may be managed in a similar way, although with more caution than the renal oncocytomas (RO). The ability to differentiate ROs from chromophobe RCCs, and from other RCCs with a greater chance of metastasis, would guide the physician and patient towards the most appropriate management, whether nephron-sparing surgical resection or conservative surveillance. Consistent accurate diagnosis of ROs is likely to remain elusive until modern molecular biomarkers are identified and applied routinely. This review focuses on the differentiation of renal oncocytomas and chromophobe RCCs. It summarises the history, epidemiology and clinical presentation of the renal neoplasms, explains the diagnostic dilemma, and describes the value, or not, of current molecular markers that are in development to assist in diagnosis of the renal neoplasms.
The incidence of renal tumours has been increasing steadily in Europe, USA and Australia over the past three decades. The widespread use of cross-sectional imaging has increased the detection of incidental smaller tumours, while the 20–30% incidence of advanced tumours has remained relatively constant. Despite current imaging techniques and the availability of renal lesion biopsy, most contemporary surgical series continue to report significant rates of benign lesions among resected small renal masses. Preoperative biopsy of these small lesions is not widely employed, and one contributing factor is potential diagnostic uncertainty in the differentiation of benign renal oncocytomas (RO) from malignant chromophobe renal cell carcinomas (chRCC) and, as an added difficulty, eosinophilic clear-cell RCCs (ccRCC). Consequently, there is a group of small renal lesions where increased confidence in characterisation may defer or obviate the need for surgical intervention. ROs and small chRCCs are two such lesions.
ChRCCs, although having a more favourable prognosis than other RCC subtypes, is a malignant tumour with the potential for metastatic spread and death. By comparison, there appears to be only one confirmed case report of metastases from ROs. Thus, due to its benign nature, ROs can usually be monitored and treated expectantly. Similarly, small renal masses found to be chRCCs may, in some situations, be suitable for active surveillance rather than immediate resection or ablation. ROs and chRCCs are often considered to be extremities of the same morphological spectrum. Proper differentiation largely relies on H&E histochemistry of sections, and an experienced histopathologist to discern the characteristic histomorphologic features between the two entities. Immunohistochemistry is used in selected instances. Electron microscopy was commonly performed in the past, but is done only in rare cases now, given the prominent overlap of staining patterns. There is also the coexistence of ROs with chRCCs seen in sporadic cases of hybrid tumours, renal oncocytosis and Birt-Hogg-Dube (BHD) syndrome. Differentiation of ROs and chRCCs, especially as small renal masses, from other more sinister forms of RCCs, like ccRCCs, is also important for the appropriate management of these patients.
Abstract and Introduction
Abstract
Standard treatment of renal neoplasms remains surgical resection, and nephrectomy for localised renal cell carcinoma (RCC) still has the best chance of cure with excellent long-term results. For smaller renal masses, especially stage T1a tumours less than 4 cm, nephron-sparing surgery is often employed. However, small incidentally detected renal masses pose an important diagnostic dilemma as a proportion of them may be benign and could be managed conservatively. Renal oncocytoma is one such lesion that may pose little risk to a patient if managed with routine surveillance rather than surgery. Additionally, lower-risk RCC, such as small chromophobe RCC, may be managed in a similar way, although with more caution than the renal oncocytomas (RO). The ability to differentiate ROs from chromophobe RCCs, and from other RCCs with a greater chance of metastasis, would guide the physician and patient towards the most appropriate management, whether nephron-sparing surgical resection or conservative surveillance. Consistent accurate diagnosis of ROs is likely to remain elusive until modern molecular biomarkers are identified and applied routinely. This review focuses on the differentiation of renal oncocytomas and chromophobe RCCs. It summarises the history, epidemiology and clinical presentation of the renal neoplasms, explains the diagnostic dilemma, and describes the value, or not, of current molecular markers that are in development to assist in diagnosis of the renal neoplasms.
Introduction
The incidence of renal tumours has been increasing steadily in Europe, USA and Australia over the past three decades. The widespread use of cross-sectional imaging has increased the detection of incidental smaller tumours, while the 20–30% incidence of advanced tumours has remained relatively constant. Despite current imaging techniques and the availability of renal lesion biopsy, most contemporary surgical series continue to report significant rates of benign lesions among resected small renal masses. Preoperative biopsy of these small lesions is not widely employed, and one contributing factor is potential diagnostic uncertainty in the differentiation of benign renal oncocytomas (RO) from malignant chromophobe renal cell carcinomas (chRCC) and, as an added difficulty, eosinophilic clear-cell RCCs (ccRCC). Consequently, there is a group of small renal lesions where increased confidence in characterisation may defer or obviate the need for surgical intervention. ROs and small chRCCs are two such lesions.
ChRCCs, although having a more favourable prognosis than other RCC subtypes, is a malignant tumour with the potential for metastatic spread and death. By comparison, there appears to be only one confirmed case report of metastases from ROs. Thus, due to its benign nature, ROs can usually be monitored and treated expectantly. Similarly, small renal masses found to be chRCCs may, in some situations, be suitable for active surveillance rather than immediate resection or ablation. ROs and chRCCs are often considered to be extremities of the same morphological spectrum. Proper differentiation largely relies on H&E histochemistry of sections, and an experienced histopathologist to discern the characteristic histomorphologic features between the two entities. Immunohistochemistry is used in selected instances. Electron microscopy was commonly performed in the past, but is done only in rare cases now, given the prominent overlap of staining patterns. There is also the coexistence of ROs with chRCCs seen in sporadic cases of hybrid tumours, renal oncocytosis and Birt-Hogg-Dube (BHD) syndrome. Differentiation of ROs and chRCCs, especially as small renal masses, from other more sinister forms of RCCs, like ccRCCs, is also important for the appropriate management of these patients.
