**2. Definition of the elderly**

#### **2.1 Chronologic aging**

The cut-off point for an adult to be considered "elder" is not well defined. According to most of the literature, age 70 years is used as a chronologic marker for definition of elderly population. This is also the age most commonly used in the clinical trials in oncology as a limit for recruitment (Balducci, 2000).

#### **2.2 Physiologic aging**

In fact, elderly should be referring to a state either than a chronological age. It is well known that with time, especially at or around 70 years of age, a number of age-related physiologic changes occur affecting the physiologic reserve of the person. Many of these changes may affect the tolerance to cancer treatment as; decreased renal and liver functions, decreased volume of distribution, immune response and intestinal absorption (Avery et al., 2009). Talking more specifically about lung function, age-related pulmonary changes include a decreased response to hypoxemia or hypercapnia, decreased elasticity of the lung tissue, increased ventilation-perfusion mismatch, and decreased forced expiratory volume (Gonzalez-Aragoneses et al., 2009).
