*2.2. Samples*

To evaluate differences in expression between malignant and corresponding normal tissue, we constructed a tissue microarray (TMA) of formalin-fixed, paraffin-embedded (FFPE) tissue blocks from 34 individuals with CCC. Three punches of each individual were analyzed: the tumor center, the tumor periphery, and the adjacent normal tissue. Samples were analyzed by two professional pathologists and the mean values were taken for statistics.

### *2.3. Clinical Parameters*

The following clinical parameters were evaluated: age, sex, overall survival from the day of diagnosis, localization (intrahepatic, perihilar, extrahepatic), growth type (mass forming, periductal, intraductal), tumor size, TNM (tumor, node, metastasis) classification, metastasis, UICC (Union Internationale Contre le Cancer), grading, etiology (Table S1).

#### *2.4. Immunohistochemical Staining of OXPHOS Complex Subunits and VDAC1 (Porin) of FFPE Tissues*

All primary antibodies (Table 1) were diluted in Dako antibody diluent with background-reducing components (Dako, Glostrup, Denmark). Immunohistochemistry was performed as described previously [20]. For antigen retrieval, the sections were immersed for 45 min in 1 mM EDTA, 0.05% Tween-20, pH 8, at 95 ◦C. Tissue sections were incubated for 30 min with the above-listed primary antibodies (Table 1).


**Table 1.** Antibodies used for immunohistochemical (IHC) staining.

a according to the manufacturer's instructions.
