Pfizer (PFE) - Get Report has agreed to buy Anacor Pharmaceuticals (ANAC) for $5.2 billion to strengthen its inflammation and immunology business, the companies announced Monday.

The all-cash deal values Anacor at $99.25 per share, or a 55% premium to the stock's closing price of $63.04 on Friday. Pfizer is buying the Palo Alto-based company primarily to gain access to Crisaborole, an anti-inflammatory drug currently under U.S. Food and Drug Administration review for the treatment of mild-to-moderate atopic dermatitis, commonly referred to as eczema.

The deal comes after Pfizer and Allergan (AGN) - Get Report cancelled their proposed $150 billion merger in early April.

"This is a very big market, this atopic dermatitis, [or] eczema," Jim Cramer, founder of TheStreet and manager of the Action Alerts PLUS portfolio, said. "I think people have to recognize that Pfizer seems to have decided that we have to buy someone."

"This is a very unusual acquisition because Pfizer has been building up its cancer franchise," Cramer said.

"I wonder whether Allergan didn't eye this property and that's why there is such a high bid," Cramer said. "I think Allergan probably took a look at these guys." Allergan is one of the AAP portfolio's holdings.

Anacor's Crisaborole--which remains under review at the FDA--is viewed as an attractive asset given that "the actual effective and safe therapies on the market right now are really limited," said an industry analyst who asked to remain unnamed.

Morningstar Inc. analyst Damien Connover added on Monday that "the safety of the drug looks solid with application site pain and minor increases in respiratory infections representing the primary adverse events, both of which appear manageable, especially in contrast to more significant side effects of long-term steroid use, which is a typical treatment option for atopic dermatitis."

While segment competition in the atopic dermatitis space is growing, Conover noted that most products in late-stage development are targeting moderate to severe patients while crisaborole is targeted at mild to moderate patients.

"We believe the acquisition of Anacor represents an attractive opportunity to address a significant unmet medical need for a large patient population with mild-to-moderate atopic dermatitis, which currently has few safe topical treatments available," said Albert Bourla, Group President of Pfizer's Global Innovative Pharma and Global Vaccines, Oncology and Consumer Healthcare Businesses. "Crisaborole is a differentiated asset with compelling clinical data that, if approved, has the potential to be an important first-line treatment option for these patients and the physicians who treat them."

New York-based Pfizer believes peak sales of Crisaborole could reach $2 billion per year. The FDA is expected to make an approval decision on the drug by Jan. 7, 2017.

Assuming the drug generates $2 billion annually or greater, the valuation for the deal is "not very high for an asset that is globally unencumbered," noted the unnamed analyst.

Pfizer anticipates financing the transaction through existing cash.

In terms of future M&A, Pfizer's top priority for growth likely lies within its oncology portfolio, said the analyst.

In fact, the company is among several of its peers said to be currently exploring a bid for cancer drug maker Medivation (MDVN) . The attraction of Medivation largely likes in the fact that there exist few interesting late-stage or already-launched oncology products in the market, the analyst said.

--Adam Feuerstein contributed to this report