A female presents with a history of progressive breathlessness. Histology shows heterogeneous patchy fibrosis with several fibroblastic foci. The most likely diagnosis is -
Presence of heterogeneous, patchy fibrosis with fibroblastic foci is characteristic of usual interstitial pneumonia (a type of idiopathic interstitial pneumonia).

Idiopathic interstitial pneumonia (Idiopathic interstitial lung disease) 

Idiopathic interstitial pneumonias (IIP) comprise a group of diffuse parenchymal lung diseases characterized by various degree of inflammation and fibrosis leading to the destruction of lung architecture.
The primary area of damage involves interstitium, but other areas become involved as the disease progresses.
Idiopathic denotes an unknown etiology; therefore known causes must be excluded by Careful history and examinations.
All IIPs share similar clinical and radiological features and are distinguished primarily by the histopathological pattern on lung biopsy.
Cryptogenic organizing pneumonia
Non specific interstitial pneumonia
Usual interstitial pneumonia
Desquamative interstitial pneumonia