It is not possible with xlsread
only.
One example of using a COM Excel object:
Let's use a simple excel sheet for example, containing text, values and formula :

Then the following code:
xlfile = 'test1.xlsx' ;
xlRange = 'B3:C6' ;
exl = actxserver('excel.application'); %// Create a COM server
exlFile = exl.Workbooks.Open( [pwd '\' xlfile] ); %'// Open the file
exlSheet1 = exlFile.Sheets.Item('Sheet1'); %// Choose the worksheet
strFormula = exlSheet1.Range(xlRange).Formula %// Read the full range
Yields a nice cell array :
strFormula =
'This is text' 'hello'
'this is value' '12.5'
'this is value' '29'
'this is formula' '=AVERAGE(C4:C5)'
If you know directly the address of a specific cell, you return a simple string:
cellFormula = exlSheet1.Range('C6').Formula %// Read a single cell
cellFormula =
=AVERAGE(C4:C5)