string cachedString;
cachedString = (string)Cache["CacheItem"];
if (cachedString == null)
{
  cachedString = "Hello, World.";
  Cache.Insert("CacheItem", cachedString);
}

Dim cachedString As String
cachedString = CStr(Cache("CacheItem"))
If cachedString Is Nothing Then
  cachedString = "Hello, World."
  Cache.Insert("CacheItem", cachedString)
End If