The most pre-cancerous condition for carcinoma colon is -
A polyp is a tumorous mass that protrudes into the lumen of the gut.
GIT polyps may be of following types

A. Non-neoplastic polyps
(i)  Hyperplastic polyps

Most common polyp of the large intestine
Has no malignant potential.

(ii) Hamartomatous polyps
(a) Juvenile polyp → No malignant potential except in Juvenile polyposis syndrome
(b) Retention polyp → No malignant potential except in Juvenile polyposis syndrome
(c) Peutz Jeghers syndrome → Polyps are not premalignant but patients are at increased risk of developing extraintestinal carcinoma of pancreas, breast, lung, ovary and uterus.

(B) Neoplastic polyps
(i) Adenomatous polyp

Tubular adenoma → Has malignant potential (villous more than tubular).
Villous adenoma → Has malignant potential (villous more than tubular).

(ii) Familial polyposis (FAP) syndrome

FAP can be further classified into

(a) Classic FAP syndrome

Typically develop 500 to 2500 colonic adenoma.
A minimum of 100 polyps (adenoma) is necessary for a diagnosis of classic FAP.

(b) Attenuated FAP

Fewer polyps (average, 30)
Risk of cancer development is usually around 50%.

(c) Gardner syndrome

Polyps + multiple osteoma + epidermal cyst + Fibromatosis.

(d) Turcot syndrome

Polyps + CNS tumor (medulloblastoma, glioblastoma).

(iii) Hereditary nonpolyposis colorectal cancer (HNPCC) syndrome

Also, known as Lynch syndrome.
Characterized by an increased risk of colorectal cancer and extraintestinal cancer particularly of the endometrium.
Familial polyposis
Hamartomatous polyps
Juvenile polyps
Hyperplastic polyps