Eosinophilic solid and cystic renal cell carcinomas have metastatic potential

Sir: We read with great interest the study by Li et al. entitled ‘Re-evaluation of 33 ‘Unclassified’ eosinophilic renal cell carcinomas in young patients’, in which the authors describe the significant degree of histological overlap between different subtypes of renal cell carcinomas (RCCs) with eosinophilic/oncocytic features occurring in young patients. This study highlights the fact that the prototypical pathological features, particularly for fumarate hydratase (FH)deficient and succinate dehydrogenase (SDH)-deficient RCCs, are often not as well-developed in younger patients, a finding also described recently by Smith et al. Li et al. also report 10 new cases of the recently described eosinophilic solid and cystic (ESC) RCC in young patients, one of which was associated with liver and lung metastases. We were particularly interested in the first reported case of metastatic disease associated with ESC RCC. A 15-year-old female patient had a multifocal and necrotic ESC RCC, measuring 9 and 4 cm, and presented with inferior vena cava involvement and pulmonary emboli. The patient developed liver metastases 2 years later despite chemotherapy treatment, and was reported to be alive with disease at 72 months. We want to report our recent experience with a second patient with ESC RCC who had metastatic disease. We received a consultation case that consisted of a 15-cm renal neoplasm in a 69-year-old woman. The surgery consisted of a radical nephrectomy, and the adrenal gland and large hilar lymph nodes were also available for review. The renal tumour had classic features of the ESC RCC with a mixture of solid tumor nodules and thin septae (Figure 1A,B). The tumour cells were large with voluminous, eosinophilic cytoplasm, large irregular nuclei and variably sized coarse basophilic inclusions in the cytoplasm. The thin septae of the cysts were lined by similar neoplastic cells with a hobnail arrangement. Immunohistochemical analysis revealed paired-box gene 8 (PAX-8) nuclear reactivity in the neoplastic cells and a predominant cytokeratin 20-positive/cytokeratin 7-negative phenotype. While the tumour was renal confined, one of three hilar lymph nodes contained a metastatic focus of RCC comprised of a solid nodule of similar neoplastic cells with abundant eosinophilic cytoplasm (Figure 2). The original descriptions of sporadic ESC RCC (as well as similar tumours in patients with tuberous sclerosis complex) suggested an indolent clinical course. These two reports now confirm that ESC RCC does have the capacity for metastatic spread. We are currently aware of approximately 60 sporadic ESC RCCs (including our personal files and published cases) with only these two cases having documented metastatic disease (approximately 3%). Additional long-term clinical follow-up studies are needed, because this is still an emerging renal entity with a A