The actor was diagnosed with the disease last month and has been having regular treatment at California's Stanford University.
Pals says Patrick's weight has plummeted, leaving him gaunt and pale. He's keeping a positive outlook but mum Patsy is desperately worried about her son.
'It breaks my heart to know he's suffering,' she tells The Sun.
'But he bears it. He's hanging in there and getting the best treatment he can. He doesn't deserve to get this. He's got such a big heart.'
Last month it was reported that Patrick only had 5 weeks to live but his doctor has confirmed this is simply not true.
'Patrick has a very limited amount of disease and appears to be responding well to treatment,' he says. 'We are considerably more optimistic.'
The star, 55, lives with his wife Lisa on a ranch in New Mexico.
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