Decrease of serum buffering capacity associated with malignant neoplasms

We have developed a new tumor marker based on the finding that cancerous sera suppress glucose utilization by cultured macrophages. Phosphofructokinase (PFK) was identified as susceptible enzyme [Naknamura et al.: JNCI 1986; 77 (in press)]. We found a high correlation between PFK inhibition and the lower buffering capacity of cancerous sera against an ATP aqueous solution and diluted acidic solutions. Sera from healthy donors changed to the PFK-suppressive type when exposed to lactate, even when followed by elimination of lactate. Lactate in cancerous sera was 1.6 times more than in normal sera. Sera from patients who tend to show acidosis, such as those with diabetes mellitus or chronic renal failure and pregnant women, also showed a lower buffering capacity as well as a higher inhibition of PFK. Although the pH method is simpler, we recommend the application of the PFK inhibition test, because this enzyme inhibition is not simply composed of a lower buffering capacity of cancerous sera, but partially of an inactivation of the enzyme through oxidation.