CA9 and metastatic malignant neoplasm in the lymph nodes: Table 2 shows the correlation between primary tumours and lymph node metastases for CA9 and Hif-1α expression. A very strong correlation was found both for CA9 (P<0.001) and Hif-1α (P<0.001). For DEC-1 no correlation was found between expression in primary tumours and in lymph node metastases (P=0.45). Linear regression analysis revealed that TCP% of the lymph node metastasis (β=0.113, P<0.001), size of the lymph node metastasis (β=0.429, P<0.001) and CA9 expression of the lymph node metastasis (β=4.088, P=0.004) were the most important determinants of ECP% of the lymph node metastases.