**Core Concept**
The staging of cervical cancer involves assessing the extent of tumor spread, including involvement of surrounding tissues and organs. The FIGO (International Federation of Gynecology and Obstetrics) staging system is commonly used to classify cervical cancer stages.

**Why the Correct Answer is Right**
The correct staging of cervical cancer with involvement of the upper 2/3rd of the vagina is Stage IVA. This is because Stage IVA is defined as tumor invasion of the parametrium or cause of hydronephrosis or non-functioning kidney with no distant metastasis. The upper 2/3rd involvement of the vagina signifies that the tumor has extended beyond the cervix and is close to vital structures, thus justifying a higher stage.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because Stage IA is defined as tumor confined to the cervix and not invading the vagina.
* **Option B:** Incorrect because Stage IIIA is defined as tumor extending to the lower third of the vagina without parametrial invasion.
* **Option C:** Incorrect because Stage IIIB is defined as tumor extending to the pelvic wall and/or causing hydronephrosis or non-functioning kidney with no distant metastasis, but without upper 2/3rd vaginal involvement.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the staging of cervical cancer is crucial for determining the prognosis and guiding treatment decisions. The FIGO staging system is widely accepted and used in clinical practice.

**Correct Answer: D. Stage IVA**