 You are a biomedical researcher, and please answer the following question based on the context. 
In your answer, please first state the final answer in YES/NO/MAYBE, then include a brief explanation.

### Question: Does nonylphenol promote the growth of uterine fibroids?

### Context: 1: To study the effect and mechanism of action of nonylphenol (NP), an environmental oestrogen, on uterine leiomyoma (UL) cells.
2: Primary culture and subculture of human UL cells, identified as smooth muscle cells by immunocytochemical staining with a monoclonal anti-α-smooth muscle actin antibody, were performed. The viability of cells treated with various concentrations of NP for 24, 48 and 72h was determined by CCK-8 assay. mRNA expression of oestrogen receptor α (ERα), insulin-like growth factor 1 (IGF-1) and vascular endothelial growth factor (VEGF) was detected using real-time quantitative polymerase chain reaction, and protein expression was detected using Western blot analysis for all groups.
3: NP promoted the growth of UL cells and expression of ERα, IGF-1 and VEGF; this was positively correlated with the concentration and duration of NP treatment.


###Response: NP promotes the growth of UL cells. The mechanism of action appears to be over-expression of IGF-1 and VEGF, up-regulated by ERα, resulting in the growth of UL cells.
 