RewriteEngine on
RewriteBase /

# Get file from Cache.
RewriteCond %{REQUEST_METHOD} GET
RewriteCond %{REQUEST_URI} .*/([^/]+\.htm)$
RewriteCond /homepages/123/htdocs/Cache/%1 -s
RewriteRule .* Cache/%1 [QSA,S=2]

# Get file via CMS.
RewriteCond %{REQUEST_METHOD} GET
RewriteCond %{REQUEST_URI} .*/([^/]+\.htm)$
RewriteCond /homepages/123/htdocs/Cache/%1 !-s
RewriteRule (.*)\.htm$ /homepages/123/htdocs/CMS.pl?PID=$1 [T=application/x-httpd-cgi,QSA,L]