\usepackage{booktabs}          %preamble
\usepackage{multirow}          %preamble    

\renewcommand{\multirowsetup}{\centering}
\begin{tabular}{cccc}
 \toprule
  Case & Box A & Box B & Remarks \\
 \midrule
  \multirow{2}{10mm}{A}
   & $+X$ & $-1.0$ & \multirow{2}{10mm}{B} \\
    \cmidrule(lr){2-3}
   & $-X$ & $-7.9$ & \\
 \bottomrule
\end{tabular}