copyTextureToTexture alpha ignored

I load a “base” texture and a “pattern” texture, when both are loaded I use the copyTextureToTexture method but “pattern” alpha is ignored so as result I have only the “pattern” texture with black spots (where there was the alpha), the code is this:

new TextureLoader().load(baseTexturePath, _base => {
_base.flipY = false;
new TextureLoader().load(pattenTexturePath, _pattern => {
_pattern.flipY = false;
this.renderer.copyTextureToTexture(new Vector2(0, 0), _base, _pattern);
const newMAT = new MeshBasicMaterial({ map: _base, opacity: 0.5, transparent: true });
_mesh.material = newMAT;

The “pattern” texture has alpha spots and is loaded correctly. It seems like that method can’t do a “stamp” of the texture according to alpha channel of the “pattern” texture.
Thanks for the help.