Latex equation not rendered properly

The latex code below does not render properly on docx2latex:
$$\begin{cases} \begin{align}
&Ns_{1} < Ns_{2} \
&S_1 = S_2
\end{align}
\end{cases} \longrightarrow (Ns_{1},S_1) $$
In particular the right arrow and the couple is not rendered.