Pap smear has a sensitivity around 50 %. So, half of people with cervical cancer will be missed: the test comes back normal, and yet cervical cancer may be there. Human Papilloma virus DNA (HPV DNA) testing is mucht more sensitive, but adequate tests may not yet easily be available.
Earkly symptoms are vaginal discharge, beeding and pain. Early here means first symptoms; it does not mean early, because these symptoms usually appear after the cancer has been growing for a while.
Apart from the problem of low sensitivity, classic pap testing has beeen criticized for it resulting in many false-positives. That is: many pap smears wil come back as abnormal, warranting further examination, while in the end nothing comes out. HPV vaccination is likely to decrease or even minimise cervical carcinoma to such extent, that the positive effects of screening will no longer outweigh the negative effects; if they have ever outweighed them at all.
Of interest is that Goodkin and Antoni observed a "modest correlation" between psychological stress and promotion of cervical intraepithelial neoplasia to invasive squamous cell carcinoma of the cervix. This correlation was "greatly enhanced by significant interactions with low levels of cooperative coping style and for high levels of premorbid pessimism, future despair, somatic anxiety, and life threat reactivity". (Goodkin, K, and M H Antoni, and P H Blaney. "Stress and hopelessness in the promotion of cervical intraepithelial neoplasia to invasive squamous cell carcinoma of the cervix." Journal of psychosomatic research 30 (1986): 67-76).