The isothiocyanates and glucosinolates in moringa do have antitumor properties. The plant is also antiviral against some known cancer causing viruses such as Epstein Barr virus.
You are right, phytoestrogens are anticancer, not cancer promoting. If phytoestrogens were cancer forming then we would have trouble from eating plants since all plants we consume contain phytoestrogens or phytoestrogen-like compounds.
Glucosinolates are also found in cruciferous vegetables and are also known to have anti-estrogenic effects. Although, they are also goitrogenic. Therefore, it would be a good idea to take something like seaweeds with the moringa to counter the goitrogenic effects. Red seaweeds, such as dulse, are particularly antiviral and anticancer.