There are two similar-looking conditions that are hard to tell apart. This could be either mite-caused galls, which are quite common on cherry (more so wild cherries than cultivated fruiting cherries) and their relatives, or an equally-common fungal disease called Peach Leaf Curl. We're leaning toward the latter.

Although sometimes drastic-looking in the leaf deformities mites create, they are not serious and don't threaten the long-term health of the plant. Treatment is not necessary (it also won't be effective once symptoms manifest, since it cannot cure ailments and reverse damage to leaves). The tree might shed those leaves early, but it should continue to grow normally, and some years mite populations are quite low.

Peach Leaf Curl can cause leaf drop of the infected foliage, but once symptoms manifest, no fungicide will have any impact. You can use the information on the page linked above to decide if treatment in a future year would be warranted. For fruit trees like peaches (which are related to cherry), treatment is usually necessary. We don't often see this condition affecting Kwanzan Cherry, or at least not to any worrisome degree.

For now, just trim off the branch tips with symptoms and discard (don't compost) the debris.

Miri