L1CAM Reliably Distinguishes Low-Grade Oncocytic Tumor from Other Eosinophilic Renal Neoplasms: A Multicenter Immunohistochemical Study with Diagnostic Implications

Figure 1. Histopathological and immunohistochemical features of LOT. (A) Hematoxylin and eosin staining of a LOT case, demonstrating the characteristic “small nested” architectural pattern with transition to stromal edema or hemorrhage (HE, 30×). (B) The tumor cells exhibit a small nested architecture with eosinophilic cytoplasm and prominent perinuclear halos (HE, 100×). (C) Nuclei show irregular nuclear contours and perinuclear halos (HE, 200×). (D) Diffuse and strong positive staining for CK7 (100×). (E) Negativity for CD117 (100×). (F) Weak/moderate nuclear positivity for GATA3 (100×).

Figure 2. Histopathological and immunohistochemical features of oncocytoma. (A) A case of oncocytoma displaying a solid/trabecular architecture (HE, 100×). (B) A different case, showing a tubular/alveolar pattern (HE, 100×). (C) An oncocytoma with a prevalent solid/trabecular architecture and focal areas composed of small nests in an edematous background (HE, 50×). (D) Oncocytoma cells slightly displaying irregular nuclear contours and thin perinuclear halos (HE, 200×). (E) Negativity for CK7, except for rare scattered and isolated cells (100×). (F) Diffuse cytoplasmic positivity for CD117 (100×).

Figure 3. Histopathological and immunohistochemical features of E-chRCC. (A) Hematoxylin and eosin staining of a E-chRCC case, demonstrating the characteristic solid/trabecular architecture (HE, 25×). (B) The tumor cells exhibit a solid architecture, with slightly eosinophilic cytoplasm and prominent perinuclear halos (HE, 100×). (C) A case of E-chRCC showing a prevalent tubular/alveolar architectural pattern (HE, 50×). (D) E-chRCC cells typically displaying irregular nuclear contours and prominent perinuclear halos (HE, 200×). (E) Diffuse and strong positive staining for CK7 (100×). (F) Diffuse cytoplasmic positivity for CD117 (100×).

Figure 4. Histopathological and immunohistochemical features of EVT. (A) Hematoxylin and eosin staining of an EVT case, demonstrating the characteristic architectural pattern, with tubular/alveolar arrangement and loose edematous stroma (HE, 50×). (B) The tumor cells exhibit eosinophilic cytoplasm with prominent intracytoplasmic vacuoles, a hallmark of EVT (HE, 100×). (C) The nuclei are often atypical, with irregular contours and distinct, prominent nucleoli (HE, 200×). (D) Negative staining for CK7 in EVT cells (100×). (E) Strong and diffuse positivity for CD117 (100×). (F) Diffuse positivity for Cathepsin K (100×).

Figure 5. L1 cell adhesion molecule (L1CAM) immunohistochemical stainings. (A) L1CAM immunostain labeling the basolateral membrane of the principal cells of medullary collecting ducts (100×). (B) A subset of cortical distal tubules showing L1CAM expression (100×). (C) Diffuse and strong membranous L1CAM staining in LOT (100×). (D–F) Negative staining for L1CAM in oncocytoma (D), E-chRCC (E), and EVT (F) cases (100×).

Figure 6. Bar plot showing the immunohistochemical expression rates (%) of CK7, CD117, GATA3, cathepsin K, and L1CAM across four renal tumor types: Low-grade oncocytic tumor (LOT), oncocytoma, eosinophilic chromophobe renal cell carcinoma (E-chRCC), and eosinophilic vacuolated tumor (EVT). L1CAM expression is exclusive to LOT, supporting its diagnostic specificity in this setting.