Extracellular lactate tends to inhibit cellular growth or enhance cell death. This happens in the vicinity of tumors and in cell cultures.
See for example this reference: Ozturk, Sadettin S., Mark R. Riley, and Bernhard O. Palsson. "Effects of ammonia and lactate on hybridoma growth, metabolism, and antibody production." Biotechnology and bioengineering 39.4 (1992): 418-431 (available here: https://www.researchgate.net/profile/Mark_Riley5/publication/227705703_Effects_of_ammonia_and_lactate_on_growth_metabolism_and_antibody_production/links/540e0bcb0cf2f2b29a3a765a.pdf)
What is the mechanism behind this effect of lactate? Why lactate has these negative effects?