Ghosh is dying from cancer. He has hidden his illness from others, but eventually he is discovered.
"Marion learns that Ghosh has been hiding that he has cancer. After much treatment and several blood transfusions, Ghosh passes away in comfort with his family and is buried next to Sister Mary Joseph Praise" (eNotes).
Secrets are a large part of the narrative in Cutting for Stone, so Ghosh's secret is part of a wider motif that explores some of the ways in which the truth can be dangerous or hurtful to others but can also be liberating.
In the case of his illness, Ghosh attempts to protect his family from the news as there is little that can be done to save him.
"Loyal to his wife and his sons, Ghosh tries to hide his illness so as not to trouble his family with worry" (eNotes).
Having experienced a number of traumatic losses already, Ghosh's concern for his family's mental and emotional well-being is justified. The twins lost their mother and father both as they were born. Hema loses Sister Mary Praise in the same episode and later loses Rosina, her maid, to suicide and loses Rosina's daughter to the revolution.
So much emotional strife has characterized the life of the family, Ghosh's decision to spare the family one more drama is arguably a well-considered secret to keep.
Yet there is reason to critically assess all the secrets the figures of the novel choose to keep. Again, the keeping of secrets is a theme in the novel and it is also a recurring statement.
“The world turns on our every action, and our every omission, whether we know it or not.”
Ghosh, dying secretly of cancer, keeps something more than a secret from his family. He keeps them from helping him, for a time, denying them a chance to suffer with him and to know him fully.