Table 1 Macroscopic, microscopic and immunohistochemical features of the samples from the three patients

Macroscopic features

Partial nephrectomy specimen of 596 g and 160 × 130 × 70 mm was 30% necrotic and composed of a cystic lesion (T1) of 110 × 110 × 70 mm with solid, friable, grey-yellow content.

Within the cystic wall, there was a reasonably well-limited nodular lesion (T2) of 20 × 15 × 15 mm, which was firm and grey-white. The non-tumorous renal parenchyma was 50 × 20 × 18 mm in size.

Surgical specimen of 86 g was fragmented. Its grouping made it possible to vaguely reconstitute a 70 × 35 × 15 mm renal fragment that was surrounded by adipose tissue and contained a renal lesion, which was ~ 38 mm in diameter, firm, and greyish-white in colour, with necrotic and cystic zones.

Surgical specimen (395 g) contained a kidney measuring 11 × 8.5 × 4.5 cm. A well-limited mid-renal tumour of 70 × 65 mm was observed, which was non-encapsulated and fleshy, had a yellow to pale grey cut surface, and did not show necrosis or thrombus in the renal vein.

Microscopic features

Two tumours, T1 and T2 were quite distinct microscopically and separated by fibrous tissue (Fig. 2A).

Tumour (T1) was a malignant neoplasm with tubulocystic architecture (Fig. 2B). The cells were large, with clear cytoplasm and irregular nuclei, and contained nucleoli that were visible at 100 × magnification (Fig. 2C).

Tumour (T2) was composed of papillae formed by fibrovascular cores that often-contained foamy macrophages and sometimes psammoma bodies (Fig. 2D). These papillae were bordered by cubic cells with weakly eosinophilic cytoplasm and rounded nuclei that contained nucleoli perceptible at 400 × magnification.

No tumour embolus was observed.

Surgical borders were intact.

Tumour (T1) represented two-thirds of the tumour volume and was inconsistently separated from another tumour (T2) by a thin fibrous septum (Fig. 3).

T1 tumour produced papillary features within a fine fibrous stroma reaction. The papillae sometimes contained foamy macrophages in their axes and were bordered by a single layer of eosinophilic cubic cells with irregular nuclei and nucleoli visible at 100 × magnification. No tumour emboli were present.

T2 tumour was composite and consisted of short bundles of spindle cells without nuclear atypia or epithelioid differentiation, vessels with thick and fibrous walls, and lobules of mature adipocytes.

Perinephric flat was devoid of tumour invasion.

There was no evidence of fibrous septa between T1 and T2 tumours (Fig. 4A).

T1 tumour consisted of large, clarified cells, with irregular nuclei containing nucleoli visible at 100 × magnification, arranged in a solid and acinar pattern.

T2 tumour was made of atypical eosinophilic cells, displaying tubes, papillae, and solid clusters.

No tumour embolus or extension in the perinephric flat was present.

Immunohistochemical features

Tumour cells of the first lesion (T1) were positive for CD10 and CA-IX, and negative for CK7 and P504S.

In contrast, tumour cells of the second lesion (T2) were positive for CK7 and P504S, and negative for CD10 and CA-IX (Figs. 2E-H).

Tumour cells of T1 were immunoreactive with CK7 but not with CD10 or CA-IX.

Spindle cells of T2 expressed smooth muscle actin, caldesmon, and HMB-45.

T1 tumour cells were positive for Vimentin, CA-IX, CD10 and PAX8, negative for CK7, P63 and CD117. In contrast, the T2 tumour cells were positive for Vimentin, CA-IX, CD117 and PAX8, negative for CK7, CD10 and P63 (Figs. 4B-C).