**Question:** Which of the following tumours have an increase elevation of placental alkaline phosphatase in the serum as well as a positive immunohistochemical staining for placental alkaline phosphatase?

A. Carcinoma of the liver
B. Carcinoma of the pancreas
C. Carcinoma of the cervix
D. Carcinoma of the colon

**Correct Answer:** C. Carcinoma of the cervix

**Core Concept:** Placental alkaline phosphatase (PLAP) is an enzyme that is expressed in a variety of tissues during pregnancy, particularly in the placenta. It is also found in some malignancies, particularly those with a gestational or trophoblastic component.

**Why the Correct Answer is Right:** Carcinoma of the cervix (Cervical cancer) is known to express placental alkaline phosphatase due to its gestational or trophoblastic component. This enzyme is elevated in the serum of patients with cervical cancer, leading to its use as a marker for this disease. Additionally, immunohistochemical staining for placental alkaline phosphatase is positive in cases of cervical cancer, confirming the presence of this enzyme in the tumor cells.

**Why Each Wrong Option is Incorrect:**
A. Carcinoma of the liver (Hepatocellular carcinoma) does not express placental alkaline phosphatase due to its hepatocellular origin. Consequently, its serum levels are not elevated and immunohistochemical staining for PLAP is negative.
B. Carcinoma of the pancreas (Pancreatic cancer) also does not express placental alkaline phosphatase due to its pancreatic origin. Its serum levels are not elevated and immunohistochemical staining for PLAP is negative.
D. Carcinoma of the colon (Colorectal cancer) does not express placental alkaline phosphatase due to its colonic origin. Its serum levels are not elevated and immunohistochemical staining for PLAP is negative.

**Clinical Pearl:** In clinical practice, elevated serum placental alkaline phosphatase levels and positive immunohistochemical staining for PLAP can help in diagnosing cervical cancer and distinguishing it from other malignancies that do not express this enzyme. This can be a valuable tool in the diagnosis and surveillance of cervical cancer.